"What does a minute cost?" is the first question in any voice agent evaluation, and everyone gets it wrong when they try to answer with a single number. Cost has at least four components, and they scale differently.
Four components
Line cost. The per-minute charge paid to the telephony operator. Domestic and international differ. On WhatsApp calls this component behaves differently; there is no international call charge.
Model cost. The usage cost of the AI model conducting the conversation. Directly proportional to call duration.
Analysis cost. Post-call summary, tagging and scoring. Effectively fixed per call.
Infrastructure and platform. A monthly fixed fee. It runs whether or not calls happen.
Why one number misleads
Two different usage patterns on the same system produce entirely different costs:
- In a business making 20 calls a day, fixed components dominate; cost per call looks high.
- In a business making 500 calls a day, fixed components spread out; cost per call drops markedly.
So "it costs this much per minute" means nothing without stating volume.
Hidden components
Three things commonly skipped when budgeting:
- Failed calls. An unanswered call can still incur a line cost. Calls that reach voicemail and leave a message are charged in full.
- Retries. Someone called three times costs three calls; in campaign planning they appear as one person.
- Test calls. The hundreds of tests made during setup inflate the first month's bill. That is normal but surprising when unexpected.
When comparing
Comparing the cost of a voice agent with the cost of people is common but must be done carefully. The right comparison is not "a rep's salary" but total cost per call handled; and on the human side there are things to include: after-hours coverage, leave, training time, idle capacity for variable volume.
Honesty also requires counting what the agent cannot do. A voice agent does not close every call; handed-over calls are still a human cost.
Three settings that lower cost
- Shortening calls. Overlong greetings, repeated sentences and excessive confirmation questions all add time. Every shortened call saves on two components at once.
- Cleaning the call list. Calls to dead numbers are a complete loss.
- Choosing the right channel. For informational contact, a written message is cheaper than a call and often more effective.
What to measure
Measure cost not per minute but per outcome: cost per appointment, cost per closed sale, cost per resolved support request. Cost per minute is an input; cost per outcome is a decision.
Tomorrow: which of these numbers should reach a manager.