Running an AI phone agent on US numbers costs four things: a monthly fee for each phone number, a per-minute telephony charge (inbound toll-free minutes cost more than inbound local minutes), a per-minute AI voice charge for speech recognition, the language model and speech synthesis, and, if the agent also sends texts, a one-off and monthly registration cost for SMS. Using published list prices from Twilio, Telnyx and Retell AI checked on 23 October 2026, the illustrations below land between roughly $60 and $2,100 a month for 1,000 to 20,000 minutes, with the AI voice layer, not the phone line, making up most of the bill.
Prices in this market change often, and every vendor quoted here says so on its pricing page. Treat the figures as a dated snapshot for budgeting, not a quote.
Key takeaways
- •The phone number is a minor cost. Twilio lists a US local number at $1.15 a month and a toll-free number at $2.15 a month; Telnyx lists both at $1.00 a month.
- •Toll-free inbound minutes cost more than local inbound minutes. Twilio lists $0.0220 a minute for inbound toll-free against $0.0085 for inbound local, roughly 2.6 times as much, because the business pays for the caller's call.
- •The AI layer dominates the bill. On the list prices checked, speech recognition, the language model and the synthetic voice together cost between about $0.05 and $0.08 a minute, against well under $0.03 for telephony.
- •SMS needs registration before it works. US carriers require A2P 10DLC registration for business texting on local numbers, and Twilio has blocked messages from unverified toll-free numbers since 31 January 2024.
- •Outbound AI calls carry legal duties. In February 2024 the FCC confirmed that AI-generated voices count as "artificial" voices under the TCPA, so consent rules apply.
The four cost components
An AI phone agent sits on top of an ordinary phone line. Each call passes through a carrier, a telephony platform, and an AI voice stack, and each layer bills separately unless you buy a bundled product.
| Component | What you pay for | How it is billed | Typical share of the bill |
|---|---|---|---|
| Number rental | Local (10-digit) or toll-free (800, 888, 877 and so on) numbers | Per number, per month | Small |
| Telephony minutes | Carrying the call over the public phone network | Per minute, inbound and outbound priced separately | Small to moderate |
| AI voice usage | Speech-to-text (STT), the large language model (LLM), text-to-speech (TTS), orchestration | Per minute, sometimes per token or character | Usually the main cost |
| SMS registration and messages | A2P 10DLC brand and campaign registration, toll-free verification, per-message fees | One-off, monthly and per segment | Only if the agent texts |
1. Number rental: local versus toll-free
A local number shows a geographic area code. A toll-free number is free for the caller, so the business carries the cost of the inbound leg. That difference shows up in the minute rate rather than the monthly rental.
Twilio also lists an emergency calling fee of $0.75 per number per month if you enable it. Most small deployments need one or two numbers, so rental rarely exceeds a few dollars a month.
2. Telephony minutes: inbound, outbound and the toll-free premium
This is where the local versus toll-free choice starts to matter.
| Rate (US list price) | Twilio | Telnyx (SIP trunking, "from") |
|---|---|---|
| Inbound to a local number | $0.0085 / min | $0.0032 / min |
| Inbound to a toll-free number | $0.0220 / min | $0.015 / min (varies by calling number) |
| Outbound to US numbers | $0.0140 / min | $0.005 / min |
| Media streaming to an AI service | $0.0044 / min (Media Streams) | $0.0035 / min (WebSockets) |
Sources: Twilio US voice pricing and Telnyx SIP trunking pricing, checked 23 October 2026. Telnyx's Voice API page also lists a $0.002 per minute platform fee on top of SIP trunking for its programmable voice product.
Two points are worth noting:
- •Toll-free inbound is the expensive leg. On Twilio, a 5,000-minute month on a toll-free number costs $110 in inbound minutes, against $42.50 on a local number.
- •Outbound minutes are priced differently again. If the agent places callbacks or reminder calls, budget the outbound rate separately.
Twilio also lists a SIP interface rate of $0.0040 per minute, which applies when calls are handed over a SIP connection, for example to an external AI voice platform. Recording, transcription, answering machine detection ($0.0075 per call on Twilio) and branded caller ID ($0.12 per call) are optional extras.
3. AI voice usage: unbundled components or a bundled platform
The AI layer does three jobs on every turn of the conversation: it transcribes the caller (STT), decides what to say (LLM), and speaks the reply (TTS). An orchestration layer handles turn-taking and interruptions. You can buy these pieces separately or as a bundle.
| Option (US list price) | What the per-minute fee covers | Published rate |
|---|---|---|
| Telnyx Voice AI | Orchestration, STT and TTS; LLM and telephony billed separately | $0.05 / min voice engine; Telnyx cites about $0.006 / min for an open model it hosts; frontier models at their own rates |
| Retell AI | Voice infrastructure, then LLM and TTS added per minute | $0.055 / min infrastructure; LLM from $0.0016 to over $0.16 / min depending on model; TTS from $0.015 / min |
| Vapi | Hosting fee; STT, LLM and TTS passed through at provider cost | $0.05 / min hosting; Vapi's own estimator shows $82 to $129 for 1,000 minutes including models |
| Twilio ConversationRelay | STT and TTS orchestration on Twilio; you bring the LLM | $0.07 / min |
Choice of model drives the spread. On Retell's list, a small model such as GPT 5 mini is $0.008 a minute while larger models run from $0.064 to $0.16 a minute. Premium voices also cost more: Retell lists $0.015 a minute for its standard voice providers and $0.04 to $0.10 a minute for ElevenLabs voices.
Two billing details catch people out:
- •Minimum increments. Telnyx notes that voice-engine charges round to 60-second increments, so a 20-second call is billed as a full minute.
- •Concurrency. Retell includes 20 simultaneous calls and lists $8 per additional concurrent call per month. A busy inbound line can need more.
4. SMS: A2P 10DLC and toll-free verification
Many AI phone agents send a text after the call, such as a booking confirmation or a link. In the US, that requires carrier registration.
On local numbers (A2P 10DLC): Twilio's brand registration documentation lists a one-time $4.50 brand registration fee and a $41.50 one-time vetting fee for Standard brands. Twilio's campaign vetting FAQ states a $15 vetting fee per campaign, and monthly campaign fees in Twilio's help centre range from $1.50 (low-volume mixed) to $10 depending on use case. Twilio's A2P 10DLC overview warns that unregistered traffic attracts additional carrier fees.
On toll-free numbers (toll-free verification): Twilio's toll-free messaging guidance states that messages from unverified toll-free numbers have been blocked since 31 January 2024. Verification is submitted through the Twilio Console or API.
Per message: Twilio's US SMS pricing lists $0.0083 per outbound or inbound segment for both long code and toll-free numbers, plus carrier pass-through fees that vary by network (for example, $0.0035 per segment for AT&T on the published table).
Registration takes time, and a rejected campaign has to be resubmitted, so it is sensible to start this process before the voice agent goes live.
A worked monthly example from list prices
The tables below are an illustration built only from published list prices checked on 23 October 2026. They are not a quote and leave out taxes, carrier surcharges, volume discounts, SMS, recording and concurrency add-ons. Every minute is assumed to be an inbound call to a single number.
Stack A: Twilio telephony plus Retell AI
Assumptions: one Twilio number; calls passed to Retell over SIP at Twilio's $0.0040 per minute SIP interface rate; Retell voice infrastructure ($0.055), GPT 5 mini ($0.008) and a standard voice ($0.015), giving $0.078 per minute for the AI layer. Retell lists no charge for custom telephony.
| Monthly minutes | Local number: total | Toll-free number: total | Difference |
|---|---|---|---|
| 1,000 | $91.65 | $106.15 | $14.50 |
| 5,000 | $453.65 | $522.15 | $68.50 |
| 20,000 | $1,811.15 | $2,082.15 | $271.00 |
How the 5,000-minute local figure is made up: $42.50 inbound minutes + $20.00 SIP + $390.00 AI layer + $1.15 number rental.
Stack B: Telnyx end to end
Assumptions: one Telnyx number at $1.00; Telnyx Voice AI engine at $0.05 per minute; the roughly $0.006 per minute LLM cost Telnyx cites for a model it hosts; inbound SIP at $0.0032 (local) or $0.015 (toll-free) per minute. This follows the components in Telnyx's own calculator example; if the $0.002 per minute Voice API platform fee applies to your setup, add $2, $10 or $40 respectively.
| Monthly minutes | Local number: total | Toll-free number: total | Difference |
|---|---|---|---|
| 1,000 | $60.20 | $72.00 | $11.80 |
| 5,000 | $297.00 | $356.00 | $59.00 |
| 20,000 | $1,185.00 | $1,421.00 | $236.00 |
What the example shows
- •The AI layer is roughly 75 to 95 per cent of the total across both stacks. Changing the model or the voice moves the bill far more than changing the number type.
- •Toll-free adds a predictable premium of roughly 15 to 20 per cent at these volumes, all of it in the inbound minute rate.
- •Costs scale almost linearly. There is little fixed cost at list price, so a quiet month costs little and a busy month costs proportionally more.
- •Switching to a frontier model changes the picture. Using a $0.064 per minute model on Retell instead of a $0.008 one would add $56 per 1,000 minutes, which on its own exceeds the whole telephony bill.
Local or toll-free: how to decide
| Consideration | Local number | Toll-free number |
|---|---|---|
| Inbound minute cost | Lower | Higher (business pays for the call) |
| Caller perception | Signals a local presence | Signals a national business |
| SMS route | A2P 10DLC registration | Toll-free verification |
| Typical use | Single-region services, clinics, trades | National support lines, e-commerce |
Many businesses run both: a local number on the website and Google Business Profile, and a toll-free number for national campaigns. Both can point to the same AI agent. If you want a wider view of what an AI receptionist costs once set-up and maintenance are included, see our AI receptionist cost guide.
Costs that sit outside the per-minute rate
The list prices above cover running costs only. A production deployment usually also involves:
- •Integration work to connect the agent to a calendar, CRM or ticketing system.
- •Prompt and knowledge-base maintenance as services, prices and policies change.
- •Monitoring and quality review of call transcripts.
- •Concurrency headroom for peak hours.
- •Compliance work for outbound calling. The FCC's February 2024 declaratory ruling confirmed that AI-generated voices fall under the TCPA's rules on artificial and prerecorded voices, so outbound campaigns need the appropriate prior consent.
None of these has a list price. They depend on the scope of the deployment, which is why vendor calculators only cover usage.
A practical budgeting method
- •Estimate monthly minutes. Multiply expected calls by average call length, then round each call up to the provider's billing increment.
- •Split inbound and outbound minutes, and split inbound again into local and toll-free.
- •Choose the AI stack and model, then take the per-minute rate from the vendor's current pricing page.
- •Add number rental and SMS registration as fixed items.
- •Add 10 to 20 per cent headroom for retries, transfers and minimum-increment rounding, and recheck prices before signing anything, since all three vendors note that rates change.
If you are comparing approaches to the telephony side, our pages on SIP and VoIP telephony and AI calling agents describe how the layers fit together.
Frequently overlooked details
- •Taxes and regulatory surcharges are added to US telephony invoices and are not shown in list prices.
- •Failed messages can still cost money. Twilio's SMS pricing page lists a $0.001 failed-message processing fee.
- •Blocked messages are billed. Twilio's documentation notes that rates apply to messages blocked from unverified toll-free numbers.
- •Volume tiers exist. Telnyx, for example, lists discounted plans with monthly minimums, so list prices overstate costs at high volume.
For broader context on where voice agents fit alongside other automated workflows, the AI automation overview is a useful next read.
Sources
- •Twilio – US voice pricing (checked 23 October 2026)
- •Twilio – US SMS pricing (checked 23 October 2026)
- •Twilio – A2P 10DLC brand registration
- •Twilio – A2P 10DLC overview
- •Twilio – A2P 10DLC campaign vetting FAQ
- •Twilio – Best practices for toll-free SMS in the US and Canada
- •Telnyx – SIP trunking pricing (checked 23 October 2026)
- •Telnyx – Voice API pricing (checked 23 October 2026)
- •Telnyx – Voice AI agent pricing (checked 23 October 2026)
- •Retell AI – Pricing (checked 23 October 2026)
- •Vapi – Pricing (checked 23 October 2026)
- •Cooley – FCC: AI-generated robocalls under the TCPA
For a plain-language look at the receptionist use case, see the AI receptionist cost guide.