The United States is the largest voice market in the world and, for international carriers, one of the most heavily regulated. Calls that would pass without comment elsewhere are blocked, labelled as spam or rejected outright in the US. This guide covers what's different: number formats, STIR/SHAKEN attestation, caller ID expectations, TCPA limits, and how US routes are tiered.
Not legal advice
This is a practical overview for operators. US telecom rules change often and penalties are large. If you run regulated outbound campaigns, get advice from a US telecom lawyer.
US numbers at a glance
The US shares country code +1 with Canada and many Caribbean countries under the North American Numbering Plan (NANP). Every number has the same shape:
| Part | Digits | Example |
|---|---|---|
| Country code | 1 | 1 |
| Area code (NPA) | 3 | 415 |
| Exchange (NXX) | 3 | 555 |
| Line number | 4 | 0123 |
On a SIP trunk, send US numbers in E.164 without the plus: 14155550123. Locally, people dial 10 digits (4155550123), or 1 plus 10 digits for long distance. Your dial plan should normalise all of these to the 11-digit form.
Toll-free and special ranges
Toll-free prefixes are 800, 833, 844, 855, 866, 877 and 888. The caller pays nothing and the number owner pays per minute. Calls to toll-free numbers from outside the US may not connect, depending on the number's settings.
Be careful with Caribbean area codes that look domestic, such as 876 (Jamaica) or 809 (Dominican Republic). They're +1 numbers but are billed as international — and are a classic target for toll fraud. Block them unless you need them.
STIR/SHAKEN in practice
STIR/SHAKEN is a framework that lets the originating carrier digitally sign the caller ID on each call. The FCC requires US voice providers to implement it on their IP networks. The signature carries an attestation level that tells the terminating carrier how much the originator vouches for the number.
| Attestation | What the signing carrier confirms | Typical effect |
|---|---|---|
| A — Full | It knows the customer, and the customer is authorised to use this number | Best treatment; least likely to be labelled spam |
| B — Partial | It knows the customer, but can't confirm they're authorised for this number | Often passes, but more exposed to labelling |
| C — Gateway | It's passing the call through and can't vouch for either | Most likely to be labelled or blocked |
Calls from outside the US arriving through an international gateway usually get C attestation, because the gateway can't verify the caller. That's a key reason international traffic to the US answers less well than domestic traffic.
How to get better attestation
- Use US numbers you actually own. Buy US DIDs and present them as caller ID. Ask your carrier whether calls from those numbers can be signed with A attestation.
- Don't rotate numbers. Cycling through many numbers to avoid spam labels is now a strong spam signal itself.
- Register your numbers with the free registration portals run by the main analytics companies that feed carrier spam-labelling systems.
- Keep call patterns natural. Very short average calls, high volume from one number and low answer rates all push your reputation down.
Our STIR/SHAKEN guide for call centres goes deeper into how labelling engines score numbers.
Caller ID expectations
US carriers and regulators expect the caller ID on every call to be:
- Valid — a real, assigned NANP number in the correct format
- Authorised — one you own or have explicit permission to use
- Callable — someone who rings it back should reach you or your business
Spoofing caller ID with intent to defraud or cause harm is illegal under the Truth in Caller ID Act, with fines per call. Presenting a random or unassigned number is also a fast way to get blocked: US carriers maintain "do not originate" lists and drop calls from invalid ranges.
At SIPTrunkHub, US traffic must use a caller ID you're authorised to present. We'll reject calls with invalid, unassigned or obviously spoofed numbers. See our acceptable use policy.
TCPA and outbound calling limits
The Telephone Consumer Protection Act (TCPA) governs automated and prerecorded calls and texts to US consumers. In outline:
- Consent: autodialled or prerecorded calls to mobiles generally require the person's prior express consent; marketing calls need prior express written consent.
- Calling hours: telemarketing calls are restricted to 8am–9pm in the callee's local time.
- Do Not Call: you must check the National Do Not Call Registry and keep your own internal do-not-call list.
- Identification: callers must identify themselves and provide a callback number.
- Opt-out: prerecorded marketing calls must offer an automated way to opt out.
Many states add their own stricter "mini-TCPA" laws with tighter hours, extra consent rules or registration requirements. Damages under the TCPA are set per call, so a single non-compliant campaign can become very expensive.
As the carrier, we don't certify your campaigns, but we will suspend traffic that generates complaints, traceback requests or signs of illegal robocalling. The US Industry Traceback Group traces suspicious calls back hop by hop, and every carrier in the chain is expected to respond.
How US routes are tiered
US termination isn't one product. Rate decks usually split it several ways.
By number type
- Landline vs mobile — mobile termination is often slightly more expensive.
- Toll-free — usually free or very cheap to dial from within the US.
- Alaska, Hawaii and the US territories — often priced separately and higher.
By jurisdiction: interstate, intrastate and "indeterminate"
US carriers charge different rates depending on whether a call stays within one state (intrastate) or crosses states (interstate). With international or IP traffic, the originating state isn't always known — calls may be billed at an indeterminate rate. Ask how your carrier handles this; it can change your effective price significantly.
By quality
| Route type | Description | Use for |
|---|---|---|
| Premium / CLI | Direct or tier-1 interconnects, caller ID delivered, best attestation available | Business calls, support, reminders, sales |
| Standard | Reputable wholesale routes with CLI | Most general traffic |
| Economy / non-CLI | Cheapest; caller ID not guaranteed | Not recommended for US business calling |
For the US specifically, CLI routes are strongly recommended — calls with invalid or missing caller ID are increasingly blocked outright. See CLI vs non-CLI routes.
Setting up a US trunk
A few US-specific settings to check in your PBX:
- Normalise dialled numbers to 11 digits starting with
1. Strip+and convert 10-digit dialling by adding1. - Set caller ID per outbound route to a US DID you own, in the same 11-digit format.
- Block high-risk +1 ranges you don't need — Caribbean area codes and premium services.
- Respect CPS limits. Dialers that burst traffic can trigger carrier limits and
503errors. See SIP error codes. - Keep CDRs for at least the period your compliance obligations require.
Our platform guides for Asterisk, FreePBX, 3CX and others include example dial patterns for NANP numbers.
Summary
- Format every US number as
1+ 10 digits on your trunk. - International traffic usually lands with C attestation; owning US numbers and presenting them consistently gives you the best chance of being answered.
- Caller ID must be valid, authorised and callable — spoofing is illegal and gets blocked.
- The TCPA limits automated and marketing calls; state laws can be stricter.
- US routes are tiered by number type, jurisdiction and quality. For business traffic, use CLI routes.
For rates, number availability and dialling details, see our United States SIP trunk page, or contact sales for a quote on your traffic.