{"slug":"callback-scheduling","title":"Callback Scheduling — Queue-Back, Scheduled Callbacks, and Virtual Hold","tags":["callback","virtual-hold","queue-back","scheduling","customer-experience"],"agent_summary":"Three callback patterns: queue-back (caller keeps place in queue without holding), scheduled callback (caller picks a specific time), and immediate callback (caller hangs up, agent dials when free). Reduces abandonment by 30-50% and lets queue time scale beyond what callers will tolerate on hold. Implemented in SWML via call termination + scheduled outbound dialing.","trigger_phrases":["callback scheduling","virtual hold","queue back","schedule callback voice","callback when available","save my place"],"runnable":true,"markdown":"\n# Callback Scheduling\n\nHold time is the single largest source of call abandonment. After 90 seconds on hold, drop rates exceed 30%; after 5 minutes, 60%+. Callback scheduling lets callers hang up while preserving their queue position or scheduling a specific time — recovering most of those abandoned interactions.\n\n## Three callback patterns\n\n### 1. Queue-back (virtual hold)\n\nCaller is in a queue. System estimates wait time. Offers: \"stay on hold, or hang up and we'll call you in about 12 minutes — you keep your place in line.\" Caller hangs up. When their turn comes, system dials them.\n\n**Best for:** unpredictable queue depth, high-volume support, time-sensitive issues where the caller wants resolution today.\n\n### 2. Scheduled callback\n\nCaller picks a future time slot. System dials them at the scheduled time. No queue concept — purely calendar-driven.\n\n**Best for:** sales callbacks, consultations, low-urgency issues, when current queue is empty but caller can't talk now.\n\n### 3. Immediate callback (callback-when-free)\n\nCaller submits a callback request. Next available agent dials them. No queue position, no specific time — just \"when an agent is free.\"\n\n**Best for:** quiet hours, after-hours signup, situations where the caller doesn't care about timing.\n\n## SWML — queue-back implementation\n\n```yaml\nversion: 1.0.0\nsections:\n main:\n - answer: {}\n - play: say:All agents are busy. Estimated wait is 12 minutes.\n - prompt:\n play: say:Press 1 to hold, or 2 to keep your place in line and we'll call you back.\n max_digits: 1\n - cond:\n when: \"${prompt_value} == '1'\"\n then:\n - connect:\n to: queue:support\n when: \"${prompt_value} == '2'\"\n then:\n - request:\n url: https://your.api/queue-callback\n method: POST\n body:\n phone: \"${call.from}\"\n queue: support\n queued_at: \"${call.created_at}\"\n position: \"${queue.position}\"\n - play: say:Got it. We'll call you back in about 12 minutes. Goodbye.\n - hangup: {}\n```\n\nThe `queue-callback` endpoint enqueues the callback into your backend:\n\n```python\n@app.route(\"/queue-callback\", methods=[\"POST\"])\ndef queue_callback():\n db.execute(\"\"\"\n INSERT INTO callback_queue (phone, queue, queued_at, position)\n VALUES ($1, $2, $3, $4)\n \"\"\", request.form[\"phone\"], request.form[\"queue\"], \n request.form[\"queued_at\"], request.form[\"position\"])\n return \"OK\"\n```\n\nA worker dequeues callbacks in order, dials them, and connects to the next available agent.\n\n## SWML — scheduled callback\n\n```yaml\n- prompt:\n play: say:When would you like us to call? Press 1 for in one hour, 2 for tomorrow morning, 3 for tomorrow afternoon.\n max_digits: 1\n- request:\n url: https://your.api/schedule-callback\n method: POST\n body:\n phone: \"${call.from}\"\n slot: \"${prompt_value}\"\n save: schedule\n- play: say:Confirmed. We'll call you at ${schedule.confirmed_time}. Have a great day.\n- hangup: {}\n```\n\nThe backend converts the slot to an absolute time:\n\n```python\n@app.route(\"/schedule-callback\", methods=[\"POST\"])\ndef schedule_callback():\n slots = {\n \"1\": now + timedelta(hours=1),\n \"2\": next_business_day_at(9, 0),\n \"3\": next_business_day_at(14, 0),\n }\n when = slots[request.form[\"slot\"]]\n schedule_callback_at(request.form[\"phone\"], when)\n return jsonify(confirmed_time=when.strftime(\"%A at %-I:%M %p\"))\n```\n\n## AI receptionist + scheduled callback\n\nFor natural-language scheduling, use an AI agent:\n\n```yaml\n- ai:\n prompt:\n text: |\n Help the caller schedule a callback. Ask for their preferred date and time.\n Today is ${now}. Use schedule_callback to confirm.\n SWAIG:\n functions:\n - function: schedule_callback\n parameters:\n type: object\n properties:\n phone: { type: string }\n when_iso: { type: string, description: \"ISO 8601 datetime\" }\n reason: { type: string }\n data_map:\n webhooks:\n - url: https://your.api/ai-schedule\n```\n\nThe AI handles \"next Tuesday at 3\" and \"tomorrow morning\" parsing natively, much better than DTMF slots.\n\n## Outbound dialer — the callback executor\n\nA worker reads the callback queue and dials at the right time:\n\n```python\nimport schedule\nimport time\nfrom datetime import datetime, timezone\n\ndef callback_worker():\n while True:\n # Get callbacks due in the next 30 seconds\n due = db.fetch(\"\"\"\n SELECT id, phone, queue, scheduled_for\n FROM callback_queue\n WHERE status = 'pending'\n AND scheduled_for <= now() + interval '30 seconds'\n ORDER BY scheduled_for\n LIMIT 5\n \"\"\")\n \n for cb in due:\n agent = find_available_agent(cb.queue)\n if not agent:\n continue # try again next loop\n \n # Place outbound call to customer\n sw_call = client.calls.create(\n to=cb.phone,\n from_=cb.business_number,\n url=f\"https://your.api/connect-callback?id={cb.id}&agent={agent.id}\",\n machine_detection=\"DetectMessageEnd\",\n )\n \n db.execute(\"UPDATE callback_queue SET status='dialing', call_sid=$1 WHERE id=$2\",\n sw_call.sid, cb.id)\n \n time.sleep(5)\n```\n\nWhen the customer answers, the SWML connects them to the agent:\n\n```python\n@app.route(\"/connect-callback\")\ndef connect_callback():\n cb_id = request.args[\"id\"]\n agent_id = request.args[\"agent\"]\n answered_by = request.form.get(\"AnsweredBy\", \"unknown\")\n \n if answered_by in (\"machine_start\", \"machine_end_beep\", \"machine_end_silence\"):\n # Customer's voicemail — leave a message\n return Response(\"\"\"\n \n We're returning your call but missed you. We'll try again, or call us back.\n \n \n \"\"\", mimetype=\"text/xml\")\n \n # Customer answered live — connect to agent\n return Response(f\"\"\"\n \n Hi, this is the callback you requested. Connecting you now.\n \n {agent_id}@pbx.example.com\n \n \n \"\"\", mimetype=\"text/xml\")\n```\n\n## Estimating wait time\n\nFor queue-back to work, callers need an accurate wait estimate. Compute from queue depth + average call duration:\n\n```python\ndef estimate_wait(queue_name):\n in_queue = db.fetch_val(\"SELECT count(*) FROM callback_queue WHERE queue=$1 AND status='pending'\", queue_name)\n avg_call_seconds = db.fetch_val(\"\"\"\n SELECT avg(extract(epoch from end_time - start_time))\n FROM calls\n WHERE queue=$1 AND end_time IS NOT NULL\n AND end_time > now() - interval '1 hour'\n \"\"\", queue_name)\n available_agents = db.fetch_val(\"SELECT count(*) FROM agents WHERE queue=$1 AND status='available'\", queue_name)\n \n if available_agents == 0:\n available_agents = 1 # assume one will free up soon\n \n seconds = (in_queue * avg_call_seconds) / available_agents\n return max(60, int(seconds))\n```\n\nCommunicate the estimate in friendly units:\n\n```python\ndef humanize_wait(seconds):\n if seconds < 120:\n return \"a minute or two\"\n if seconds < 600:\n return f\"about {seconds // 60} minutes\"\n if seconds < 1800:\n return \"10 to 30 minutes\"\n return \"about an hour\"\n```\n\n## Confirmation SMS\n\nAfter a callback is scheduled, send an SMS confirming:\n\n```python\nsend_sms(\n to=cb.phone,\n from_=cb.business_number,\n body=f\"Callback scheduled for {cb.scheduled_for.strftime('%A at %-I:%M %p')}. Reply CANCEL to cancel.\",\n)\n```\n\nLets caller cancel without re-calling. Reply handler:\n\n```python\n@app.route(\"/sms-inbound\", methods=[\"POST\"])\ndef sms_inbound():\n body = request.form[\"Body\"].strip().upper()\n from_ = request.form[\"From\"]\n \n if body in (\"CANCEL\", \"STOP CALLBACK\"):\n db.execute(\"UPDATE callback_queue SET status='cancelled' WHERE phone=$1 AND status='pending'\", from_)\n send_sms(to=from_, body=\"Callback cancelled.\")\n \n return Response(\"\", mimetype=\"text/xml\")\n```\n\n## Reminders\n\nFor scheduled callbacks, send a reminder SMS 15 minutes before:\n\n```python\n# Cron every minute\nupcoming = db.fetch(\"\"\"\n SELECT * FROM callback_queue\n WHERE status='pending'\n AND scheduled_for BETWEEN now() + interval '14 minutes' AND now() + interval '16 minutes'\n AND reminded = false\n\"\"\")\n\nfor cb in upcoming:\n send_sms(to=cb.phone, body=f\"Reminder: callback in 15 minutes at {cb.scheduled_for.strftime('%-I:%M %p')}\")\n db.execute(\"UPDATE callback_queue SET reminded=true WHERE id=$1\", cb.id)\n```\n\n## Compliance — caller-initiated callbacks\n\nA callback the caller specifically requested is **not telemarketing**. TCPA's robocall rules apply only to unsolicited calls. Caller-initiated callbacks are explicitly consented and exempt.\n\nHowever:\n\n- Quiet hours still apply (8 AM - 9 PM caller's local time, federal default)\n- Opt-out must still be respected if the caller ever says STOP or hangs up multiple callbacks\n- Records of consent should be retained (the original IVR/AI interaction is the consent record)\n\n## Failure modes\n\n| Failure | Cause | Recovery |\n|---|---|---|\n| Customer doesn't answer callback | Number went to voicemail | Leave VM, schedule retry in 2 hours, allow up to 3 retries |\n| Agent unavailable when customer answers | Agent went unavailable in the gap | Connect to next available agent or apologize and reschedule |\n| Customer rejects callback (\"don't call me\") | Caller changed mind | Mark as opt-out, suppress future callbacks |\n| Estimated wait too short, customer angry | Estimate algorithm bad | Tune average duration calculation, add buffer |\n\n## Common pitfalls\n\n- **No callback worker monitoring** — queue backs up silently when the worker dies. Alert on `callback_queue.status='pending' AND scheduled_for < now() - interval '5 minutes'`.\n- **Dialing outside business hours** — caller requested callback for \"tomorrow morning\" but you dial at 6 AM. Constrain to allowed hours.\n- **No abandonment after failed callbacks** — caller answered 3 times, declined each time. Stop dialing.\n- **Caller ID mismatch** — outbound caller ID different from the number they originally called. Confusing — they don't recognize it. Use the same number.\n- **Long initial confirmation** — caller is impatient. Keep it under 10 seconds.\n\n## Cost comparison — hold vs callback\n\nHold cost per call:\n\n- 15-minute hold = 15 minutes of inbound billing = ~$0.13 at $0.0085/min\n- Higher abandonment, lost revenue\n\nCallback cost per call:\n\n- 30-second inbound + outbound 5-minute call = ~$0.08\n- Lower abandonment, retains the lead\n\nCallback is cheaper and converts better. Almost always the right call.\n\n## Related patterns\n\n- [Missed call workflows](/topic/missed-call-workflows) — automated SMS after caller hangs up\n- [Call routing strategies](/topic/call-routing-strategies)\n- [Business hours logic](/topic/business-hours-logic) — constrain callback times\n- [SignalWire call flow builder](/topic/signalwire-call-flow-builder) — visual queue-back patterns\n\n## References\n\n- TCPA 47 USC §227 — caller-initiated exemption\n- ContactBabel research on hold abandonment thresholds\n- ITU-T E.412 — Network management — Operational guidance for international intelligent network\n","html":"

Callback Scheduling

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Hold time is the single largest source of call abandonment. After 90 seconds on hold, drop rates exceed 30%; after 5 minutes, 60%+. Callback scheduling lets callers hang up while preserving their queue position or scheduling a specific time — recovering most of those abandoned interactions.

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Three callback patterns

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1. Queue-back (virtual hold)

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Caller is in a queue. System estimates wait time. Offers: \"stay on hold, or hang up and we'll call you in about 12 minutes — you keep your place in line.\" Caller hangs up. When their turn comes, system dials them.

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Best for: unpredictable queue depth, high-volume support, time-sensitive issues where the caller wants resolution today.

\n

2. Scheduled callback

\n

Caller picks a future time slot. System dials them at the scheduled time. No queue concept — purely calendar-driven.

\n

Best for: sales callbacks, consultations, low-urgency issues, when current queue is empty but caller can't talk now.

\n

3. Immediate callback (callback-when-free)

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Caller submits a callback request. Next available agent dials them. No queue position, no specific time — just \"when an agent is free.\"

\n

Best for: quiet hours, after-hours signup, situations where the caller doesn't care about timing.

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SWML — queue-back implementation

\n
version: 1.0.0\nsections:\n  main:\n    - answer: {}\n    - play: say:All agents are busy. Estimated wait is 12 minutes.\n    - prompt:\n        play: say:Press 1 to hold, or 2 to keep your place in line and we'll call you back.\n        max_digits: 1\n    - cond:\n        when: \"${prompt_value} == '1'\"\n        then:\n          - connect:\n              to: queue:support\n        when: \"${prompt_value} == '2'\"\n        then:\n          - request:\n              url: https://your.api/queue-callback\n              method: POST\n              body:\n                phone: \"${call.from}\"\n                queue: support\n                queued_at: \"${call.created_at}\"\n                position: \"${queue.position}\"\n          - play: say:Got it. We'll call you back in about 12 minutes. Goodbye.\n          - hangup: {}\n
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The queue-callback endpoint enqueues the callback into your backend:

\n
@app.route(\"/queue-callback\", methods=[\"POST\"])\ndef queue_callback():\n    db.execute(\"\"\"\n        INSERT INTO callback_queue (phone, queue, queued_at, position)\n        VALUES ($1, $2, $3, $4)\n    \"\"\", request.form[\"phone\"], request.form[\"queue\"], \n       request.form[\"queued_at\"], request.form[\"position\"])\n    return \"OK\"\n
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A worker dequeues callbacks in order, dials them, and connects to the next available agent.

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SWML — scheduled callback

\n
- prompt:\n    play: say:When would you like us to call? Press 1 for in one hour, 2 for tomorrow morning, 3 for tomorrow afternoon.\n    max_digits: 1\n- request:\n    url: https://your.api/schedule-callback\n    method: POST\n    body:\n      phone: \"${call.from}\"\n      slot: \"${prompt_value}\"\n    save: schedule\n- play: say:Confirmed. We'll call you at ${schedule.confirmed_time}. Have a great day.\n- hangup: {}\n
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The backend converts the slot to an absolute time:

\n
@app.route(\"/schedule-callback\", methods=[\"POST\"])\ndef schedule_callback():\n    slots = {\n        \"1\": now + timedelta(hours=1),\n        \"2\": next_business_day_at(9, 0),\n        \"3\": next_business_day_at(14, 0),\n    }\n    when = slots[request.form[\"slot\"]]\n    schedule_callback_at(request.form[\"phone\"], when)\n    return jsonify(confirmed_time=when.strftime(\"%A at %-I:%M %p\"))\n
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AI receptionist + scheduled callback

\n

For natural-language scheduling, use an AI agent:

\n
- ai:\n    prompt:\n      text: |\n        Help the caller schedule a callback. Ask for their preferred date and time.\n        Today is ${now}. Use schedule_callback to confirm.\n    SWAIG:\n      functions:\n        - function: schedule_callback\n          parameters:\n            type: object\n            properties:\n              phone: { type: string }\n              when_iso: { type: string, description: \"ISO 8601 datetime\" }\n              reason: { type: string }\n          data_map:\n            webhooks:\n              - url: https://your.api/ai-schedule\n
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The AI handles \"next Tuesday at 3\" and \"tomorrow morning\" parsing natively, much better than DTMF slots.

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Outbound dialer — the callback executor

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A worker reads the callback queue and dials at the right time:

\n
import schedule\nimport time\nfrom datetime import datetime, timezone\n\ndef callback_worker():\n    while True:\n        # Get callbacks due in the next 30 seconds\n        due = db.fetch(\"\"\"\n            SELECT id, phone, queue, scheduled_for\n            FROM callback_queue\n            WHERE status = 'pending'\n            AND scheduled_for <= now() + interval '30 seconds'\n            ORDER BY scheduled_for\n            LIMIT 5\n        \"\"\")\n        \n        for cb in due:\n            agent = find_available_agent(cb.queue)\n            if not agent:\n                continue  # try again next loop\n            \n            # Place outbound call to customer\n            sw_call = client.calls.create(\n                to=cb.phone,\n                from_=cb.business_number,\n                url=f\"https://your.api/connect-callback?id={cb.id}&agent={agent.id}\",\n                machine_detection=\"DetectMessageEnd\",\n            )\n            \n            db.execute(\"UPDATE callback_queue SET status='dialing', call_sid=$1 WHERE id=$2\",\n                       sw_call.sid, cb.id)\n        \n        time.sleep(5)\n
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When the customer answers, the SWML connects them to the agent:

\n
@app.route(\"/connect-callback\")\ndef connect_callback():\n    cb_id = request.args[\"id\"]\n    agent_id = request.args[\"agent\"]\n    answered_by = request.form.get(\"AnsweredBy\", \"unknown\")\n    \n    if answered_by in (\"machine_start\", \"machine_end_beep\", \"machine_end_silence\"):\n        # Customer's voicemail — leave a message\n        return Response(\"\"\"\n            <Response>\n                <Say>We're returning your call but missed you. We'll try again, or call us back.</Say>\n                <Hangup />\n            </Response>\n        \"\"\", mimetype=\"text/xml\")\n    \n    # Customer answered live — connect to agent\n    return Response(f\"\"\"\n        <Response>\n            <Say>Hi, this is the callback you requested. Connecting you now.</Say>\n            <Dial>\n                <Sip>{agent_id}@pbx.example.com</Sip>\n            </Dial>\n        </Response>\n    \"\"\", mimetype=\"text/xml\")\n
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Estimating wait time

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For queue-back to work, callers need an accurate wait estimate. Compute from queue depth + average call duration:

\n
def estimate_wait(queue_name):\n    in_queue = db.fetch_val(\"SELECT count(*) FROM callback_queue WHERE queue=$1 AND status='pending'\", queue_name)\n    avg_call_seconds = db.fetch_val(\"\"\"\n        SELECT avg(extract(epoch from end_time - start_time))\n        FROM calls\n        WHERE queue=$1 AND end_time IS NOT NULL\n        AND end_time > now() - interval '1 hour'\n    \"\"\", queue_name)\n    available_agents = db.fetch_val(\"SELECT count(*) FROM agents WHERE queue=$1 AND status='available'\", queue_name)\n    \n    if available_agents == 0:\n        available_agents = 1  # assume one will free up soon\n    \n    seconds = (in_queue * avg_call_seconds) / available_agents\n    return max(60, int(seconds))\n
\n

Communicate the estimate in friendly units:

\n
def humanize_wait(seconds):\n    if seconds < 120:\n        return \"a minute or two\"\n    if seconds < 600:\n        return f\"about {seconds // 60} minutes\"\n    if seconds < 1800:\n        return \"10 to 30 minutes\"\n    return \"about an hour\"\n
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Confirmation SMS

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After a callback is scheduled, send an SMS confirming:

\n
send_sms(\n    to=cb.phone,\n    from_=cb.business_number,\n    body=f\"Callback scheduled for {cb.scheduled_for.strftime('%A at %-I:%M %p')}. Reply CANCEL to cancel.\",\n)\n
\n

Lets caller cancel without re-calling. Reply handler:

\n
@app.route(\"/sms-inbound\", methods=[\"POST\"])\ndef sms_inbound():\n    body = request.form[\"Body\"].strip().upper()\n    from_ = request.form[\"From\"]\n    \n    if body in (\"CANCEL\", \"STOP CALLBACK\"):\n        db.execute(\"UPDATE callback_queue SET status='cancelled' WHERE phone=$1 AND status='pending'\", from_)\n        send_sms(to=from_, body=\"Callback cancelled.\")\n    \n    return Response(\"\", mimetype=\"text/xml\")\n
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Reminders

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For scheduled callbacks, send a reminder SMS 15 minutes before:

\n
# Cron every minute\nupcoming = db.fetch(\"\"\"\n    SELECT * FROM callback_queue\n    WHERE status='pending'\n    AND scheduled_for BETWEEN now() + interval '14 minutes' AND now() + interval '16 minutes'\n    AND reminded = false\n\"\"\")\n\nfor cb in upcoming:\n    send_sms(to=cb.phone, body=f\"Reminder: callback in 15 minutes at {cb.scheduled_for.strftime('%-I:%M %p')}\")\n    db.execute(\"UPDATE callback_queue SET reminded=true WHERE id=$1\", cb.id)\n
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Compliance — caller-initiated callbacks

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A callback the caller specifically requested is not telemarketing. TCPA's robocall rules apply only to unsolicited calls. Caller-initiated callbacks are explicitly consented and exempt.

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However:

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Failure modes

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| Failure | Cause | Recovery |\n|---|---|---|\n| Customer doesn't answer callback | Number went to voicemail | Leave VM, schedule retry in 2 hours, allow up to 3 retries |\n| Agent unavailable when customer answers | Agent went unavailable in the gap | Connect to next available agent or apologize and reschedule |\n| Customer rejects callback (\"don't call me\") | Caller changed mind | Mark as opt-out, suppress future callbacks |\n| Estimated wait too short, customer angry | Estimate algorithm bad | Tune average duration calculation, add buffer |

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Common pitfalls

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Cost comparison — hold vs callback

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Hold cost per call:

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Callback cost per call:

\n\n

Callback is cheaper and converts better. Almost always the right call.

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Related patterns

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References

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