build.allanninal.dev

Part 6 of 7 · Voice agent series ~4 min read

What the voice agent costs

Voice is more expensive than the other systems on this blog. There’s a real phone number to pay for, and listening and speaking aren’t free. But it’s still less than a human receptionist by a lot — and the system sleeps when the phone isn’t ringing.

Anatomy of a typical monthly bill: three tiers and a total Three columns side by side. The left column, “Always free”, lists the small bookkeeping pieces — Lambda function runs, queues, alerts, small DynamoDB tables — each at no cost. The middle column, “Fixed every month”, lists the unavoidable monthly charges: the business phone number itself (about $22 per month for a claimed number), Secrets Manager at about 40 cents per secret, and S3 storage at cents per month. The right column, “Grows with call time”, lists the per-minute and per-call costs that scale with how often the phone rings: Connect inbound minutes, the listener (streaming transcription), the speaker (text-to-speech synthesis), and the AI brain on each call. Below all three columns, a wide total bar reads: total, about $35 to $50 per month at typical SMB volume of around 200 call minutes per month. Bottom note: the phone number is the floor; everything else scales with how often the phone rings. Where the dollars go in a typical month Always free $0 Lambda runs free Queues, alerts free Small tables free Webhook URLs free all under the perpetual free tier Fixed each month ~ $23/mo Phone number ~$22 Password vault ~$0.40 each S3 storage cents the phone number is the floor Grows with call time ~ $10–$25/mo Call minutes ~2¢/min Listening ~2¢/min Speaking ~3¢/min AI brain cents/call scales with how often it rings Total, typical month about $35–$50 / month at SMB volume ~200 call minutes/month; budget alarm at $80 catches anything weird The phone number is the floor. Everything else scales with how often it rings.
Fig 6. Three tiers of cost. The phone number sets the floor; per-minute costs are where heavy use shows up.

The phone number

Voice has one cost the other systems on this blog don’t: a real phone number that callers can dial. The cloud rents you one for a flat monthly fee — about a couple of tens of dollars a month, depending on the region and whether it’s a regular number or a toll-free one.

This is the floor of your bill. Even if no one ever calls, you pay this every month. There’s no way around it — phone numbers cost money to keep alive, and that’s true whether the line answers as your AI agent or as a human receptionist.

Per-minute costs

Three small per-minute costs add up while a call is in progress:

  • Call minutes. The cloud charges roughly a couple of cents per minute the line is in use. Common across all phone services.
  • Listening. There’s a per-minute charge for turning voice into text — another couple of cents.
  • Speaking. There’s a per-character charge for turning text back into voice. For a typical reply, that comes out to a few cents per minute of conversation.

Together, these run about a nickel to a dime per minute of actual call time. A 5-minute call costs around 25 to 50 cents.

AI per call

The brain charges per call, not per minute — pennies per call at the volumes this kind of system handles. A typical SMB getting 50 calls a month might pay around 50 cents to a dollar in AI fees total.

Three traps you’re avoiding

  • No always-on server — would be $30+ a month before answering anything. The voice agent only spends compute when the phone is actually ringing.
  • No managed voice-AI service — specialist voice-bot platforms charge $50+ per month with a per-minute markup on top. This is cheaper at the bottom and stays cheaper as you scale.
  • No infinite logs — 7-day retention. Logs can’t pile into a slow-growing surprise bill.

When this stops being cheap

The math turns at high volume. If your line is taking thousands of call minutes a month, the per-minute costs add up — you might be looking at $200 a month or more.

At that point you’re competing with the cost of an actual receptionist, which might be the right answer. But for the SMB this design targets — a line that rings a few dozen times a day, mostly with simple questions — the agent stays cheaper than any human option, by a wide margin.

In plain words

Phone-bill territory at typical small-business volume. The phone number alone is most of the bill until call time gets serious. Set a budget alarm that fits your expected volume and the bill can’t surprise you.

All posts