SIP Trunk in United States — New York, Los Angeles or Chicago Inbound + Outbound

1. What a SIP trunk in United States actually is

A SIP trunk is how you send and receive calls with DIDHub. Your PBX, AI voice agent, or softphone authenticates to the trunk once, and from then on every call to and from your US numbers rides it: signaling over SIP, audio over RTP. It is the modern replacement for the physical phone lines a PBX used to plug into.

What the trunk buys you is capacity: the number of calls you can have running at the same time. Each simultaneous call uses one channel (one channel = one concurrent call, inbound or outbound). Every US DID includes 2 channels out of the box; when you need more concurrency you add capacity, either dedicated to a specific number or shared as a pool across some or all of your numbers. Outbound calls draw on the same capacity.

A United States SIP trunk is that same trunk carrying +1 US DIDs allocated under FCC. You can run more than one trunk (for example one per site, brand, or environment). DIDHub provides the trunk authentication and SIP transport and coordinates FCC-compliant number allocation through our in-region carrier partners, so your platform sees a standard SIP trunk while we handle the regulator-side paperwork.

2. United States regulation: FCC, KYC, compliance

United States requires only light KYC: toll-free numbers need a RespOrg relationship and most carriers ask for basic business verification, but there's no heavy regulator filing like the strict markets. Geographic and toll-free numbers activate fast (instant once verification clears). DIDHub handles the carrier-side checks.

What people typically use a United States SIP trunk for:

• Local presence in the US for sales, support or marketing campaigns without opening a US office.
• Trust signal for US buyers, a New York 212 number on your website converts dramatically better than +44 or +972 for US-targeted campaigns.
• National brand presence with toll-free 800/833/844/855/866/877/888, free for callers, signals scale.
• Marketing campaign tracking, a unique US number per ad/source to measure attribution.
• Move an existing US landline to a modern VoIP/Teams setup via port-in.

The US is the easiest country in the world to get a virtual phone number in. No KYC, no proof of address, no US residency, no business registration. The Federal Communications Commission (FCC) does not require end-user verification for ordinary number allocation. STIR/SHAKEN attestation requirements apply at the carrier level, DIDHub handles that for you. Result: you check out and the number is yours, live in seconds.

For the broader picture across countries, see our guide to international DID compliance & KYC bundles. For the SIP-trunk concept end-to-end, see the DID Number Provider guide.

3. Number types you can route over the trunk

DIDHub supports the standard United States number types over the SIP trunk:

For a deeper look at how number types differ globally, see DID number types explained.

4. How DIDHub's SIP trunk works in United States

The technical surface of the trunk is standardised; the United States-specific choices are the POP, the codec list, and the failover topology.

Ingress POPs

• Washington, DC (primary), lowest in-region latency to United States endpoints.
• San Jose (failover), secondary route used if the primary path degrades.

Transport & security

• TLS:5061 recommended for any production trunk; UDP allowed for legacy.
• SRTP for media via DTLS-SRTP or SDES.
• SIP authentication: digest registration (PBX behind NAT) or IP-ACL (static peering). See SIP authentication.

Codecs

• G.711 μ-law (PCMU), the default in North America.
• G.722, wideband HD voice on capable endpoints.
• Opus, for AI voice agents and IP-native softphones.
• G.729, available on request.

For the codec deep-dive, see voice codecs explained.

DTMF

• RFC 4733 (telephone-events over RTP) is the default. SIP INFO and in-band DTMF available for legacy interop on request.

Channel concurrency

• One channel = one concurrent call, inbound or outbound. The channel count is your simultaneous-call capacity, the standard way to size a trunk.
• Every DID includes 2 channels, so basic two-way calling works with nothing extra to buy.
• Need more? Add capacity. Extra channels can be dedicated to a single DID (reserved for that number, never starved) or shared as a pool across all or a chosen subset of your numbers (most cost-efficient when numbers peak at different times). Outbound draws on the same capacity.
• Capacity scales to 200+ per trunk off the shelf, and you can run multiple trunks for hard separation. See multiple concurrent calls on one DID.

STIR/SHAKEN

• STIR/SHAKEN is mandatory for US/Canada outbound. DIDHub-allocated numbers are signed with A-attestation by default, the strongest trust signal under the US/CA framework. Mobile carriers increasingly mark non-A calls as “Spam Likely”, see STIR/SHAKEN and spam labels.

5. Outbound calling from your United States trunk

Outbound from a United States-allocated DID to United States destinations is allowed within approved use cases. The per-minute economics:

Outbound caller-ID rules

• Your outbound CLI must match a DID you've allocated through the trunk. Setting an arbitrary caller ID is rejected at the SBC.
• Origin-based rating (OBR) applies on cross-border outbound, the regulated EEA tier may apply depending on the source carrier.
• For multi-region operators, see origin-based rating savings.

6. Setup in 6 steps

Asterisk pjsip example

; /etc/asterisk/pjsip.conf
[transport-tls]
type=transport
protocol=tls
bind=0.0.0.0:5061
cert_file=/etc/asterisk/keys/asterisk.crt
priv_key_file=/etc/asterisk/keys/asterisk.key
method=tlsv1_2

[didhub-united-states]
type=auth
auth_type=userpass
username=YOUR_DIDHUB_USERNAME
password=YOUR_DIDHUB_PASSWORD

[didhub-united-states]
type=aor
contact=sip:sip.didhub.io:5061;transport=tls
qualify_frequency=30

[didhub-united-states]
type=endpoint
transport=transport-tls
context=from-didhub
disallow=all
allow=g711u,g722,opus
outbound_auth=didhub-united-states
aors=didhub-united-states
dtmf_mode=rfc4733
media_encryption=sdes
direct_media=no

3CX SIP trunk template snapshot

# 3CX -> SIP Trunks -> Add SIP Trunk -> Generic SIP Trunk
Trunk name:        DIDHub United States
Registrar:         sip.didhub.io
Transport:         TLS
Port:              5061
Authentication:    Register/Account based
Auth ID:           YOUR_DIDHUB_USERNAME
Auth password:     YOUR_DIDHUB_PASSWORD
Outbound caller ID: +1 ... (one of your allocated DIDs)
Codecs (priority):  G.711u / G.722 / Opus

7. Integration patterns

Every modern PBX, UC platform, and AI voice stack can authenticate against the trunk:

8. Pricing

Four line items: per-DID monthly rental, per-minute inbound usage on every United States DID (even landline geographic numbers carry an inbound MOU charge in United States), channel capacity, and per-minute outbound. Setup is $0 once FCC paperwork is approved.

Per-DID monthly

Channel capacity

Per-minute outbound

See section 5 above and the full global rate sheet.

9. Porting an existing United States number

Existing United States number? Porting timeline is 1-3 weeks.

• Typical port time: 1-3 weeks
• Required documents: phone bill + LOA + ID + proof of address (FCC requirements)
• Cost: port-in fee per number; carrier-side fees may apply

For the full porting playbook (US/UK/EU + the global gotchas), see number porting explained.

10. FAQ

Which POP should I connect to for a United States SIP trunk?

Washington, DC is the recommended primary; San Jose is the standard failover. Both terminate to United States via in-region carriers.

How long does activation take for a United States SIP trunk?

Instant after KYC documents are accepted (or instantly where KYC isn't required). Provisioning the SIP side itself is hours, not days; the variability is on the FCC/carrier side.

What codecs should I configure for a United States SIP trunk?

G.711u / G.722 / Opus as the negotiation list, in that order. G.711u is the regional default for United States interop.

Can I use my United States SIP trunk with Microsoft Teams?

Yes, via Microsoft Teams Direct Routing through DIDHub's managed SBC. See Teams Direct Routing.

Can I use my United States SIP trunk with AI voice agents (Vapi, Retell, ElevenLabs)?

Yes, BYOC SIP trunk works with every major AI voice platform. Bind specific United States DIDs to specific agents; outbound CLI must match an allocated DID.

How many concurrent calls can one United States DID handle?

Every DID includes 2 channels, so 2 concurrent calls (inbound or outbound) out of the box. To go higher you add capacity and either dedicate it to that DID (reserved for that number) or share a pool across several of your numbers. One channel is one concurrent call in either direction.

Can I have more than one SIP trunk?

Yes. Many customers run several trunks, for example one per site, brand, environment, or PBX. Capacity can be dedicated to a trunk or a specific DID, or shared from a common pool across your account.

Does STIR/SHAKEN apply in United States?

Yes · A-attestation default. DIDHub-allocated US/CA numbers are signed with A-attestation by default.

Can I port my existing United States number to a DIDHub SIP trunk?

Yes. Typical United States port timeline is 1-3 weeks. Required documents vary by number type; contact us for the specific checklist. See number porting explained for the global picture.

What use cases get approved most easily?

Customer service inbound, opted-in callbacks, transactional 2FA, inbound AI voice agents, and Microsoft Teams Direct Routing for registered entities. Cold outbound, unsolicited SMS campaigns, and anonymous-relay setups are routinely rejected.

11. Related country pages