Robocall Mitigation

Robocall mitigation is the layered apparatus that carriers, federal regulators, and third-party analytics providers use to block, label, or downrank unwanted calls. Calls flagged as "Spam Likely" see answer rates drop 50-80%. Application developers operate inside this system and must build for it.

The layered ecosystem

                    Originating carrier (signs with STIR/SHAKEN)
                                   ↓
                    Intermediate carriers (pass through, may add tags)
                                   ↓
                    Analytics providers (Hiya, First Orion, TNS, YouMail)
                                   ↓
                    Terminating carrier (applies tags, may block outright)
                                   ↓
                    Recipient's phone (displays tag, allows answer)

Each layer makes independent decisions. A call rated "trusted" by your originating carrier can still be flagged "Spam Likely" by the terminating carrier based on independent reputation data.

The TRACED Act and the FCC RMP

The Pallone-Thune TRACED Act of 2019 requires:

All US carriers implement STIR/SHAKEN on IP-based networks by 2021-06-30 (see STIR/SHAKEN)
Carriers without full STIR/SHAKEN deployment must file a Robocall Mitigation Plan (RMP) in the FCC database
Terminating carriers must verify or block calls from carriers not registered in the RMP database
FCC empowered to fine non-compliant carriers up to $10,000 per violation and revoke STI-CA certificates

For voice service providers, RMP registration is mandatory. For application platforms (SignalWire, Twilio), the originating carrier (the platform) handles compliance.

The four analytics tag providers

Most carriers contract with one of these for reputation scoring:

| Provider | Carrier customers | Branded tag | |---|---|---| | Hiya | Samsung, AT&T (partial), T-Mobile (partial) | "Spam Risk" / "Scam Risk" | | First Orion | T-Mobile (Scam Shield), some MVNOs | "Scam Likely" | | TNS (Transaction Network Services) | Verizon (Call Filter), AT&T (Call Protect) | "Telemarketer" / "Spam Risk" | | YouMail | Free consumer app, also carrier-licensed | "Robocaller" / "Scam Caller" |

A call gets a "Spam Likely" tag when:

Recent call volume from the number is high
Average call duration is very short (typical for unanswered robocalls)
Recipients have manually marked it as spam
The number's reputation across analytics databases is negative
STIR/SHAKEN attestation is missing or low

Per-carrier mitigation programs

T-Mobile Scam Shield

Tags suspected spam as "Scam Likely"
Blocks high-confidence scam calls outright (caller hears busy signal)
Free for all T-Mobile subscribers, premium tier ($4/mo) adds caller ID and reverse lookup
Aggressive — false positive rate ~15-25% on legitimate business calls

AT&T Call Protect

Tags as "Spam Risk" or "Telemarketer"
Blocks confirmed fraud automatically
Free baseline, premium tier adds enhanced caller ID

Verizon Call Filter

Free baseline + premium tier
Tags as "Potential Spam" or "Spam Likelihood: High/Medium/Low"
Custom block lists per user

Comcast Xfinity Mobile

Uses Verizon's Call Filter (MVNO)

What gets a number tagged

Empirically, in the first 30 days after a number is provisioned, reputation forms based on:

| Signal | Impact | |---|---| | Volume of outbound dials | High volume + low answer rate = bad reputation | | Average call duration | Very short (< 10 sec) = likely robocall | | Diversity of destinations | Calling many unrelated numbers in a small window = bad | | Manual user spam reports | Single biggest negative signal | | STIR/SHAKEN attestation level | Attestation A protects, C hurts | | Caller ID consistency | Changing caller ID mid-campaign = bad | | Geographic mismatch | LA number calling Phoenix mostly = neutral, calling random country codes = bad | | Time-of-day pattern | Calling 2 AM local time = bad |

Application-developer playbook

What you can do as someone running SignalWire or other voice platforms:

1. Set up brand reputation early

Hiya Connect — submit your business profile, get caller ID branding shown
First Orion ENGAGE — similar branded caller ID program
TNS Origin Identification — branded business calling

Branded caller ID shows your business name + logo on the recipient's phone, bypassing "Unknown Caller" and "Spam Likely" tags.

2. Match caller ID to actual number ownership

If your caller ID is +13105551234, your outbound traffic should originate from a network that legitimately owns that number. STIR/SHAKEN Attestation A requires this.

3. Pace outbound dialing

Most carriers' reputation engines flag:

100 dials per minute from one number
1000 unique destinations per hour from one number
5000 short-duration (< 10 sec) outbound calls per day from one number

Pace below these thresholds. Spread campaigns across many numbers with similar profiles.

4. Improve answer rates

A number's reputation improves when calls get answered and conversations happen. Low answer rates ("ghost callers") drive reputation down.

Tactics:

Match area code to caller's region ("snowshoeing" is bad — see below)
Use voicemail drop appropriately when answered by machine (so the call counts as "attempted" not "abandoned")
Provide opt-in proof to carrier dispute resolution teams to fight false positives

5. Snowshoeing is bad

Snowshoeing means using many different numbers to spread call volume evenly so no single number trips reputation thresholds. Carriers detect this via:

Many numbers calling from the same SBC (Session Border Controller)
Similar dial patterns
Same content (when sampled by analytics)

When detected, the whole number range gets flagged together. Don't snowshoe. Build reputation per number organically.

6. Submit dispute requests

If your legitimate business number gets tagged "Spam Likely":

| Carrier | Dispute path | |---|---| | AT&T (TNS) | https://www.callprotect.tns.com/ | | Verizon (TNS) | Same TNS portal | | T-Mobile (First Orion) | https://callscoreinfo.com/ | | Hiya | https://www.hiya.com/business | | YouMail | https://directory.youmail.com/ |

Submit business documentation. Resolution: 5-30 business days. Re-tagging is possible if behavior continues to look spammy.

7. Number rotation strategy

Rotate numbers every 30-90 days for outbound campaigns. Reputation deteriorates gradually with sustained outbound; fresh numbers start clean. Don't rotate so fast that you can't build branded caller ID.

8. Avoid TCPA-flagged content

Carrier analytics inspect the audio of recorded sample calls. "Free trial," "you've been selected," "limited time offer" trigger ML models that flag the number.

SignalWire-specific guidance

Number reputation visibility

SignalWire doesn't expose analytics-provider scores directly. Check externally via:

https://www.nomorobo.com/lookup — free
https://www.tellows.com/ — community-rated
https://www.hiya.com/business — paid

If a number is consistently labeled "Spam Likely" across multiple lookups, retire it.

STIR/SHAKEN with SignalWire

SignalWire automatically signs outbound calls with Attestation A when the number is owned by the project. For BYOC scenarios, attestation may drop. See STIR/SHAKEN.

Caller ID branding

SignalWire integrates with Hiya, First Orion, and TNS for branded caller ID. Setup is via SignalWire support — submit your brand info and they provision via the analytics provider.

Common failure modes

| Symptom | Cause | Fix | |---|---|---| | New number gets "Spam Likely" within days | Snowshoeing detected, or content flagged | Pace dialing, vary content, register with analytics providers | | Branded caller ID not showing despite registration | Analytics provider hasn't propagated yet (24-72 hours) | Wait, re-confirm in lookups | | T-Mobile blocks outright but other carriers don't | T-Mobile Scam Shield is most aggressive | Submit dispute, reduce volume, vary content | | Answer rate dropped 40% overnight | Number got flagged | Lookup reputation, dispute if false positive, rotate to clean number if not | | Calls "completed" but actually ringing-then-blocked | Carrier blocked at terminating switch | CDR will show short duration; cross-check with carrier |

When to retire a number

Retire when:

Reputation lookup shows persistent spam tagging
Answer rate < 30% for 2+ weeks after operational changes
Recipient feedback shows the number is being filtered

Retire by stopping outbound and either reassigning to inbound-only use or releasing back to the carrier pool (after 30 days, the next subscriber inherits a fresh reputation).

Toll-free and short codes are safer

Toll-free numbers (after TFV) and short codes have much stronger reputation footing because:

They're explicitly registered business numbers
Carriers know they're A2P channels and apply different filtering rules
Recipients trust them more

For high-volume outbound that survives carrier filtering, toll-free or short code is often the right answer. See toll-free vs short code.

Related patterns

STIR/SHAKEN — caller ID attestation framework
Voicemail drop — pace outbound to avoid reputation hits
Call quality metrics — diagnose if "calls are completing" but actually being blocked
Toll-free vs short code — alternatives for high-volume outbound

References

TRACED Act of 2019 — Pub. L. 116-105
47 CFR §64.6300-§64.6308 — STIR/SHAKEN and RMP implementing rules
FCC Robocall Mitigation Database — https://fccprod.servicenowservices.com/rmd
Hiya Connect, First Orion ENGAGE, TNS Origin ID — vendor documentation
Industry Traceback Group — voluntary investigation framework

Robocall Mitigation — Carrier Filtering, RMP Filings, and Analytics Tags