| name | twilio-numbers-senders |
| description | Choose the right Twilio number type and sender BEFORE building. Covers phone numbers (local, toll-free, short code, mobile), alphanumeric sender IDs, WhatsApp senders, RCS agents, international availability, and regulatory bundles. Each number type has its own compliance program — choosing wrong means rebuilding. Use this skill first.
|
Overview
Choosing the right number type and sender is the first decision in any Twilio project. Each number type comes with its own compliance/verification program, throughput limits, and capabilities. Developers who skip this step buy numbers first, build their app, then discover they chose the wrong type.
Lifecycle: Choose numbers/senders (this skill) → Register them (twilio-compliance-onboarding) → Follow traffic rules (twilio-compliance-traffic)
US Number Types — Comparison
| Local (10DLC) | Toll-Free (800/888/877) | Short Code (5-6 digits) |
|---|
| SMS | Yes | Yes | Yes |
| MMS | Yes | Yes | Yes |
| Voice | Yes | Yes | No |
| Two-way | Yes | Yes | Yes |
| Throughput | ~1-75+ SMS/sec (varies by trust score) | ~3 SMS/sec | 10-100 SMS/sec |
| Compliance program | A2P 10DLC (brand + campaign) | Toll-Free Verification | Pre-approved at purchase (carrier review) |
| Approval timeline | 10-15 business days | 3-5 business days | 8-12 weeks provisioning |
| Best for | Transactional, marketing, support | Notifications, support, verification | High-volume marketing, 2FA |
| Cost | Lowest | Medium | Highest (setup + monthly + per-msg) |
Source: US/Canada SMS comparison
Compliance Programs Per Number Type
Every US number type requires its own verification before traffic flows:
-
Local 10DLC → A2P 10DLC registration: Brand registration (EIN, business identity) + Campaign registration (use case, sample messages, opt-in flow). Trust Score determines throughput. Sole Proprietors: ~1 SMS/sec, 1 campaign. Standard: ~15+ SMS/sec, scales with secondary vetting. A2P overview | Quickstart
-
Toll-Free → Toll-Free Verification (TFV): Business name, website, use case description, sample messages, opt-in type. Unverified toll-free numbers cannot send SMS to US/Canada. Console onboarding | Requirements
-
Short Code → Carrier review at purchase: Application reviewed during 8-12 week provisioning. Available in 14 countries: US, Canada, UK, Germany, France, India, Brazil, Mexico, Argentina, Colombia, Dominican Republic, New Zealand, Spain, Sweden. Short code guidelines by country | What is a short code?
-
Twilio Verify → Exempt. No registration needed — Verify handles compliance automatically.
See twilio-compliance-onboarding for full registration details and gotchas.
How to Choose (US)
- Need voice + SMS from same number? → Local (10DLC) or toll-free. Short codes are SMS-only.
- Marketing at scale (>15 SMS/sec)? → Short code (highest throughput) or 10DLC with secondary vetting + Messaging Service number pool
- Fastest time to send? → Toll-free (3-5 day verification) or Twilio Verify (immediate, no registration)
- Customer support with local presence? → Local number in customer's area code
- Transactional notifications? → Toll-free (simpler registration) or 10DLC
- Verification OTPs? → Twilio Verify (exempt from A2P, built-in Fraud Guard)
- Budget-constrained? → 10DLC (lowest cost) — but plan for 10-15 day registration
Non-Phone Senders
Alphanumeric Sender IDs
A branded name (up to 11 characters) displayed instead of a phone number. One-way only — recipients cannot reply.
- Not supported in the US or Canada
- Supported in 100+ countries; some require pre-registration with documentation
- Some carriers impose minimum length — short IDs may display as "unknown"
- Add to Messaging Services for automatic sender selection by destination country
Docs: Alpha Sender in Messaging Services | International support by country | How to register
WhatsApp Business Senders
A phone number registered with Meta's WhatsApp Business Platform via Twilio.
- Requires WABA (WhatsApp Business Account) + sender approval
- Outbound requires pre-approved Message Templates (outside 24-hour service window)
- Direct customers: self-service Console signup or Senders API
- ISVs: Meta Tech Provider Program for customer onboarding
Docs: WhatsApp hub | Getting started | Self sign-up
RCS Agents
Branded sender with logo, rich cards, carousels, and suggested actions. Falls back to SMS automatically.
- Requires carrier-level approval per country
- Testing phase: RCS only delivers to added test devices; others get SMS fallback
- Each RCS sender can only belong to ONE Messaging Service
Docs: RCS onboarding | RCS compliance guide | Regional availability
Voice Trust: Number Reputation Programs
If making outbound voice calls, these programs improve answer rates:
| Program | What it does | Carriers | Prerequisites |
|---|
| STIR/SHAKEN | Level A attestation = trusted caller ID | US and Canada | Trust Hub Business Profile + EIN |
| Voice Integrity | Remediates spam/scam labels | T-Mobile, AT&T, Verizon (coming) | Approved Business Profile + US address |
| Branded Calling | Shows name + logo on caller ID | T-Mobile, Verizon (Public Beta) | STIR/SHAKEN + Trust Hub profile |
| CNAM | Displays business name on caller ID | US long codes only (not toll-free) | EIN or DUNS number |
Priority order: STIR/SHAKEN first (required for Level A attestation) → Voice Integrity (spam label remediation) → Branded Calling (visual caller ID, mobile only) → CNAM (simplest, lowest impact, landlines by default).
Docs: STIR/SHAKEN overview | Voice Integrity overview | Branded Calling overview | CNAM overview
Branded Calling: Prerequisites & Display Standards
The call trust stack is layered — each product builds on the one below:
Layer 4: Enhanced Branded Calling (name + logo + call reason)
↑ requires
Layer 3: Basic Branded Calling (business name display)
↑ requires
Layer 2: Voice Integrity (spam label remediation)
↑ requires
Layer 1: SHAKEN/STIR (attestation — auto-applied with approved profile)
↑ requires
Layer 0: Primary Customer Profile (Trust Hub business identity)
Prerequisites for Basic Branded Calling:
- Approved Primary Customer Profile in Trust Hub (EIN, business name, address, authorized rep) — 1-3 business days
- SHAKEN/STIR — automatic once profile is approved
- Signed Letter of Authorization (LOA) for the phone numbers
- Basic Branded Calling trust product submitted + approved — 2-4 weeks
Additional prerequisites for Enhanced Branded Calling:
5. Approved Voice Integrity trust product — 3-7 business days carrier propagation
6. Enhanced Branded Calling trust product — 3-6 weeks
Phone number eligibility:
- Local and mobile numbers only — toll-free numbers are NOT eligible
- Must be Twilio-owned (not ported-in numbers pending transfer)
- Calls must originate via Programmable Voice (API or TwiML) — SIP Trunking calls are not branded
- Each number can only belong to one Branded Calling trust product at a time
Display standards:
| Asset | Basic | Enhanced |
|---|
| Display name | Business name, ~32 char carrier limit, must match Trust Hub profile | Same |
| Logo | N/A | Square, min 300x300px, max 1MB, PNG/JPG, no text overlays |
| Call reason | N/A | Free-text, ~40 char carrier display limit (e.g., "Appointment Reminder") |
Display name rules:
- Must match registered business name or documented trade name/DBA
- No phone numbers, URLs, or special characters
- Misleading names are rejected during review
Call reason guidelines (Enhanced only):
- Must accurately describe the call purpose
- Cannot be generic ("Important Call") or misleading
- Set per trust product — cannot be changed per-call
- Keep under 40 characters for consistent carrier display
Carrier support:
- T-Mobile: Basic + Enhanced (native)
- AT&T, Verizon: Voice Integrity spam remediation; Branded Calling display expanding
- Apple/iOS: Enhanced only, limited support
CNAM (traditional caller ID): 15-character limit, text-only, works on landlines, propagates in 24-48 hours, no approval process needed.
International Numbers
- ~25 countries have GA (self-service) SMS numbers. Many major markets are Private Offering — requires a request form and 1-6 week delivery.
- MMS only available in US, Canada, and Australia. Use WhatsApp or RCS for rich media elsewhere.
- Many countries require Regulatory Bundles (identity/address verification) before provisioning numbers. Non-compliant numbers risk deprovisioning.
Docs: Country SMS guidelines | Regulatory compliance | How to submit a bundle | Country regulatory requirements
CANNOT
Phone Numbers
- No mobile number type in the US —
availablePhoneNumbers('US').mobile.list() returns 404. US numbers are classified as local or toll-free only.
- Cannot use both
voiceApplicationSid and voiceUrl — Setting one auto-clears the other. Same for smsApplicationSid vs smsUrl.
- Cannot use
voiceApplicationSid and trunkSid simultaneously — Setting one auto-deletes the other.
contains pattern requires minimum 2 characters — Single-character patterns return 400. Wildcards * mid-pattern also fail.- Geographic search is US/Canada only —
nearNumber, nearLatLong, inPostalCode, inRegion, inRateCenter, inLata are ignored for non-US/CA numbers.
- No undo for number release — Once released, the number goes back to the pool. No grace period or reclaim mechanism.
- Address required for many international numbers —
addressRequirements can be none, any, local, or foreign. Purchase fails without the required address/bundle.
Voice Trust
- Cannot guarantee call delivery — Carrier spam filters operate independently. Even Level A + Branded Calling + Voice Integrity can still be filtered.
- Cannot brand inbound calls — Branded Calling applies to outbound calls only.
- Cannot use Voice Integrity or Branded Calling outside the US — Voice Integrity and Branded Calling are currently US-only. STIR/SHAKEN is available in the US and Canada (CRTC-mandated since Nov 2021).
- Cannot bypass manual approval — Trust Hub vetting involves human review (1-3 business days for profiles, 2-6 weeks for Branded Calling).
- Cannot preserve attestation through
<Dial> — CallToken forwarding requires the Calls API or Conference Participants API.
- Cannot use Branded Calling with SIP Trunking — Calls must originate via Programmable Voice.
- Cannot use toll-free numbers with Branded Calling — Local and mobile numbers only.
Common Mistakes
- Buying numbers before understanding compliance — Each number type has its own registration program. Choosing 10DLC means 10-15 days of A2P registration before you can send.
- Using local numbers for marketing without A2P — Messages get filtered (error 30034). All US 10DLC requires A2P registration.
- Expecting toll-free to work immediately — Unverified toll-free numbers cannot send SMS to US/Canada at all.
- Assuming MMS works internationally — Only US, Canada, Australia. Use WhatsApp or RCS elsewhere.
- Choosing short code for voice — Short codes are SMS/MMS only. No voice capability.
Next Steps
- Register your numbers:
twilio-compliance-onboarding
- Set up Messaging Services with number pools:
twilio-messaging-services
- Follow traffic rules after registration:
twilio-compliance-traffic
- WhatsApp sender management:
twilio-whatsapp-manage-senders
