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Reference · telephony for agents

Phone numbers for an agent line.

If you are giving an AI agent its own phone number, the choice is mostly made on four numbers — what the number costs per month, what each text costs, how hard it is to open the account, and whether the provider lets a one-person business register for US business texting. Everything else is either the same across vendors or is a sales call.

Rates re-checked at each vendor's own pricing pages on 8–9 October 2026 (USD, US local numbers). Where a vendor does not publish a figure, the cell says so rather than guessing. Telecom pricing moves; treat this as a snapshot, not a quote.

Side by side

Seven services, in the order a solo builder would sensibly consider them. The last two are in here because people ask about them for this job and they are the wrong tool for it.

US market, list prices, excluding taxes and carrier pass-through where the vendor bills them separately.
Service Number cost / mo Per-SMS cost Signup friction 10DLC sole-proprietor path Best for
Telnyx carrier + API in one company $1.00 local toll-free from $1.00 · +$0.10/mo to switch SMS+MMS on $0.004 per part out + carrier pass-through · $0.004 in · published per carrier (≈$0.0035 AT&T, $0.0045 Verizon) Low for a machine Web form asks for company details, which reads business-first. There is a documented agent signup API: bot challenge → bot signup → emailed magic link → API key. No LinkedIn, no work-email gate. Yes $4.50 brand + $15 campaign vetting + $2/mo. One campaign per brand, one number per campaign; ~1,000 msgs/day to T-Mobile, 15 msgs/min to AT&T. The cheapest API-native SMS for an agent line that only has to send and receive text.
Twilio the default, priced like it $1.15 local leased toll-free $2.15/mo $0.0083 per segment out same inbound · + carrier fees · $0.001 per message that ends Failed Lowest Verified on the live signup form: first name, last name, email, password — and a "sign up with Google" button. No company fields. Yes $4.50 brand + $15 campaign vetting + $2/mo. No EIN and no SSN: identity is confirmed by one-time passcode to a US/CA mobile number. One number per campaign. Getting an account open today. Most expensive per message of the three API-first options. Trial accounts can text only verified numbers until you upgrade.
Plivo cheapest pair, hardest door $0.50 long code toll-free $1.00/mo $0.0077 per SMS out same inbound · toll-free $0.0079 · carrier surcharges published (AT&T $0.0035, T-Mobile $0.0045, Verizon $0.0050) Higher The console login labels the field "Work Email", and new accounts go through "Request a trial account" rather than instant signup. Their main pricing page now lists SMS under Enterprise (from $1,000/mo); the SMS rate card still publishes these pay-as-you-go figures. Yes, via a starter path Standard registration is $4.50 brand (+$41.50 optional vetting) + $15 campaign vetting + $10/mo. Plivo's starter-registration docs (no tax ID) quote $4.50 + $15 vetting + $2/mo campaign. The cheapest number-plus-message pair of the three, if you can get through the trial gate.
Vonage enterprise messaging, sales-led Not verified — 2026-10-08 Public pricing pages sat behind a bot challenge today, so no figure is quoted here. Vonage routes number pricing to a downloadable sheet and an account conversation. Not verified — 2026-10-08 Their own docs point at a country-by-country spreadsheet and a per-account pricing API rather than a rate card. High Account pricing is a sales conversation; the docs assume you already have an account. Published and standard: $4.50 brand + $41.50 brand vetting (Aegis/WMC) + $15 per campaign vetting event + $1.50–$30/mo campaign subscription, three-month minimum. Sole-proprietor campaigns are exempt from the external brand vetting step. Teams already inside the Vonage ecosystem. Weakest fit for a single agent line.
Bandwidth direct-to-carrier, built for volume $0.35 per line from their own comparison table; full product pricing is "available on request" $0.004 per 10DLC SMS out toll-free $0.007 · short code $0.008 · MMS $0.015 · inbound shown as free in their comparison table Highest Request-a-quote form with company and headquarters fields; messaging is sold as an enterprise contract. Published, but priced for programs: $8 one-time sole-proprietor brand + $4/mo campaign (Standard campaign is $20/mo, three-month minimum). High-volume platforms that can commit to a contract. Overkill for one number.
SignalWire the agent should answer the phone $0.50 local toll-free $0.80 · port-out $5. Voice minutes are extra, not a substitute for the number. $0.00415 per 10DLC SMS same inbound · toll-free $0.00680 · carrier fees extra Self-serve Hosted SDK and APIs, pay-as-you-go from the site. Standard carrier registration applies. Voice on those numbers is $0.0066/min inbound, $0.0080/min outbound. Letting an AI actually answer calls on a flat $0.16/min runtime (STT + LLM + standard TTS + orchestration), plus transport. Also a working SMS carrier, just not the cheapest.
Photon iMessage relay, not a carrier $25 Pro (managed shared pool) free tier shared pool · $250/line/mo for a dedicated iMessage line Not a per-SMS carrier. Plain SMS/RCS is a stated fallback, not the product. Self-serve Tiered plans straight from the pricing page. Not applicable — this traffic does not ride 10DLC. You cannot bring your own number on the consumer tiers, and on the dedicated tier you own the line. Blue-bubble iMessage, if that is genuinely required. The wrong tool for plain SMS.

Voice agents, side by side

Eleven ways to give an agent a phone account that answers calls, cheapest all-in minute first. The number itself is the smallest line on every one of these bills.

US local numbers, list prices, pay-as-you-go tiers, read at each vendor’s own pages on 9 October 2026. Sorted cheapest all-in minute first; click any header to re-sort. Where a vendor publishes no figure, the cell says so.
Service ≈ All-in / min▲ Number / mo▲ Inbound / min▲ Outbound / min▲ Signup▲ Best for▲
Plivocheapest minutes, hardest door $0.033 $0.03 runtime (models, transcription, orchestration) + $0.0028 inbound $0.50 local; toll-free $1.00 $0.0028 local; toll-free $0.0120 $0.0046 local, “starts at”; Alaska $0.1770 Higher work-email gate; trial request The cheapest number-plus-minute pair and the cheapest agent runtime, if you can get through the trial gate.
LiveKit Cloudopen-source agents, hosted $0.0479 $0.01 session + $0.01 telephony + $0.0179 models + $0.01 observability $0.00 one free number, then $1.00/mo · toll-free $2.00 $0.0100 US local; 50–1,000 min included by plan Not published third-party SIP, $0.004/min to connect Self-serve no card; 1,000 agent minutes free Hosting an open-source LiveKit Agents stack with a phone number attached and paying only for what runs.
Telnyxcarrier, API and GPUs in one company $0.06 voice engine $0.05 + inbound $0.0032 + LLM ≈$0.006 $1.00 local; volume from $0.79 · toll-free from $1.00 $0.0032 SIP trunk local; toll-free from $0.015 $0.005 SIP trunk local; toll-free routes free Self-serve card on file, provisioned by API Carrier, API and inference GPUs on one invoice. Cheaper than Twilio on the minute, more expensive than Plivo and LiveKit.
Twiliothe default, priced like it $0.0785 relay $0.07 + inbound $0.0085, before model tokens $1.15 local; toll-free $2.15 — their price CSV $0.0085 local; trunking $0.0034 · toll-free $0.0220 $0.0140 US & Canada; toll-free the same — their price CSV Lowest name, email, password or Google Opening an account today and integrating with almost anything. Most expensive minute of the API-first options.
ElevenLabs Agentsbest voices, you supply the carrier $0.08 per call minute; model and carrier extra You bring it no telephony fee; connect Twilio or SIP Your carrier’s a separate invoice at its own rate Your carrier’s a separate invoice at its own rate Self-serve 15 free call minutes; plans from $6 Voice quality on top of a carrier you already run. Telephony and the model are two more invoices; burst minutes cost double.
Vapirent the orchestrator, pick your models $0.082 hosting $0.05 + models $0.032; range to $0.129 $0.00 1 included; 5 on Core ($29/mo) $0.008 Twilio; Telnyx $0.0055; own SIP free $0.014 Twilio; Telnyx $0.0055; own SIP free Self-serve $5 free credits; $29/mo Core Choosing your own STT, LLM and voice per agent while someone else runs the orchestration. Models bill at cost, so the total moves with your choices.
Retell AIpick your model, pay by the minute $0.087 infra $0.055 + TTS $0.015 + LLM $0.0016+ + carrier $0.015 $2.00 $10 one-time to verify; BYO carrier free $0.015 US via Twilio $0.015 US via Twilio Self-serve $10 credits; 20 concurrent calls Per-agent model choice with someone else running the infrastructure. Denoising, guardrails and PII removal are each priced on top.
Bland AIone rate that includes the models $0.14 models included; $0.12 + $299/mo on Build $0.00 inbound number included, valued at $15/mo Pass-through your carrier, or Bland’s Twilio at cost Pass-through as above; no transfer fee on BYO Self-serve no card; 100 calls/day cap A predictable per-minute rate with the models included. Watch the $299/mo platform fee on Build and the daily cap on Start.
SignalWireone flat runtime, transport at cost $0.163 runtime $0.16 + transport $0.003–$0.008 $0.50 local (10DLC); toll-free $0.80 $0.0066 PSTN; SIP or WebRTC $0.0030 $0.0080 PSTN; SIP or WebRTC $0.0030 Self-serve hosted SDK, pay-as-you-go One flat runtime rate that includes the speech, the model and the orchestration, and the fewest moving invoices.
VonageAI Studio, billed per session Per session AI Studio Standard is $0/mo (10 agents, 10K sessions); Advanced $1,100/mo. NLU/Knowledge AI $0.00855 per request, plus Voice API rates. No per-minute runtime. Not verified numbers tab 404s; bot challenge 9 Oct $0.00485 domestic PSTN inbound $0.00849 domestic US; SIP and WebRTC $0.00492 Sales-led zone rates via a sales contact Teams already inside Vonage. AI Studio exists, but it is priced per session, not per minute, so it does not sort against the others.
Synthflowenterprise only, no published rate Not published enterprise contracts from $30,000/yr Not sold telephony inside the contract Not published no rate card Not published no rate card Sales call annual contract, scoped by volume Nothing, for a single agent line. In here as the example of a platform that has left self-serve behind.

What the all-in column is

It is what a live US inbound call costs per minute once the agent is talking: the voice runtime plus transport, and model tokens where the vendor bundles or publishes them. Where a vendor prints its own estimate, that is the figure; where it publishes only components, the two in this table that had to be added up are set out below. Twilio and ElevenLabs quote a runtime and leave the model tokens on your own bill, so their minute is only the whole story once you know what your LLM costs.

How the two added-up minutes were built

LiveKit’s figure is their own calculator default with observability switched on: session $0.0100 + US local telephony $0.0100 + LLM $0.0014 + STT $0.0075 + TTS $0.0090 + observability $0.0100. Turn observability off and it is $0.0379. Retell’s is their cheapest published components added together: voice infrastructure $0.055 + TTS $0.015 + LLM from $0.0016 + US telephony $0.015. Their own worked example is $0.15 with a mid-tier model, and the published range runs to $0.31.

The number is never the expense

Every US local number in this table costs between nothing and $2.15 a month. At 1,000 minutes a month the minutes cost $33 at the cheapest end and $163 at the bundled end, so the number is a rounding error. Choose on the per-minute rate, on whether the provider will let an agent answer at all, and on how many invoices you want to reconcile.

Where the door is a sales call

Synthflow’s page now lists only Enterprise from $30,000 a year. Vonage AI Studio has a free Standard tier, but the Advanced plan is $1,100/mo and Fully Managed is a sales conversation. Bandwidth is not in this table because it sells Bring-Your-Own-AI, not a runtime. Self-serve tonight: Telnyx, Twilio, Plivo (trial gate), LiveKit, SignalWire, Vapi, Retell, Bland or ElevenLabs.

Bringing your own carrier

The overlay platforms (Vapi, Retell, ElevenLabs, Bland, LiveKit) will run on a number you already own over SIP. Vapi charges nothing for its own SIP and $0.0055/min for Telnyx transport; Retell, ElevenLabs and Bland add nothing for custom telephony. LiveKit is $0.004/min to connect third-party SIP. Telnyx, Twilio, Plivo and SignalWire are the carriers. Buying carrier and runtime separately is usually cheaper per minute; buying them bundled is one invoice.

What is the same no matter who you pick

Registration is mandatory, not optional

Since 3 February 2025, US carriers block unregistered application-to-person traffic on ten-digit long codes outright. Not filtered, not throttled — blocked. Your messages do not arrive on an unapproved number.

Every US provider routes this through The Campaign Registry, a private company in McLean, Virginia, that the carriers appointed to keep the register. It is not a government agency. The rules it enforces are the industry's own best practices, written by the CTIA trade group and applied by the carriers.

The bill is about the same everywhere

Realistically: $4.50 brand registration, $15 campaign vetting, $2 a month per campaign on the sole-proprietor path. Standard brands pay more — around $46 at brand level plus $10 a month — and buy much higher throughput with it.

Switching providers does not avoid any of this. The fees are passed through from the registry and the carriers at cost, so vendor choice barely moves them.

Consent is where the government comes in

The FCC's role is consent, not registration. The Telephone Consumer Protection Act allows $500 in damages per non-compliant message, tripled to $1,500 for wilful violations. Marketing texts need prior express written consent.

Registration and consent are separate requirements. A perfectly registered campaign that texts people who never opted in is still exposed.

Sole proprietor or standard brand — pick once

The sole-proprietor path exists so a person without an EIN can register at all. It is capped: one campaign per brand, one number per campaign, roughly 1,000 messages a day to T-Mobile and 15 a minute to AT&T, and the cap cannot be lifted by paying for vetting.

If you already have an EIN, providers require you to register as a standard or low-volume standard brand instead. That costs more and buys far more throughput — the right answer for an agent that will actually talk to people at scale.

Bottom line

For a single agent line that texts, Telnyx is the cheapest per message among the self-serve APIs and the only one with a signup path written for a machine. Twilio is the fastest to open and the most expensive per message of those three; Plivo is cheaper on the number, dearer per text than Telnyx, and makes you ask for a trial.