Most comparisons of voice agents end up in the same spreadsheet: three vendors in three columns, a row for each capability, and a price at the bottom. The column with the lowest number wins.
The spreadsheet is usually useless, and it is useless for a reason that has nothing to do with the numbers. The prices are not in the same unit. One vendor sells minutes, one sells resolved calls, one sells seats, one sells a flat monthly fee. Putting them side by side and reading the bottom line is choosing between a price per kilo and a price per litre.
The unit is not a detail in the contract. It is the contract. It decides who carries the risk when volume moves, what the vendor makes money on the system doing, and what happens to the invoice the day the deployment starts to work.
When it works, the bill grows
Twilio's second-quarter figures are a useful illustration. The company reported 1.5 billion dollars in revenue, up 22 percent year on year. Voice revenue grew more than 20 percent. Self-service voice – the customers who set something up themselves without going through a sales meeting – grew more than 50 percent, which the company itself describes as an indicator of experimentation among smaller businesses.
In the same review, Twilio says two other things. CEO Khozema Shipchandler describes the market as being in "very early innings" and stresses that the great majority of customer interactions are still handled by humans. And the company points out that rising carrier pass-through fees are putting pressure on its smallest customers, because costs are becoming harder to forecast.
Those are not three pieces of news. They are one piece of news seen from three angles. In a market where price follows usage, "it works" and "the bill is growing" are the same event. Twilio mentions a customer that went from low six-figure quarterly spending to a six-million-dollar annual run rate. That is a success story in the vendor's quarterly deck and a budget line at the customer.
Neither of those is unreasonable. The point is that the relationship between them is rarely settled during procurement, because the unit being traded in is barely discussed at all.
Four units, four distributions of risk
| Unit | The vendor profits from | Volume risk sits with | Where it breaks down |
|---|---|---|---|
| Per minute | Calls lasting longer | The buyer | A slow agent costs more than a fast one |
| Per resolved call | Calls being completed | The vendor | Someone has to define "resolved" |
| Per seat or user | More people getting access | The buyer | Measures the headcount the agent removes |
| Flat monthly fee | You using less than you pay for | The vendor | The risk premium is paid in quiet months too |
The left-hand column is the only one most quotes state. The right-hand column is the only one that shows up in production.
The minute pays for time, not for outcome
A concrete calculation makes it clear. A call that takes sixty seconds today, and an agent that spends twenty seconds extra confirming, repeating and searching: that is a third more cost for exactly the same task. Nothing in the contract gives the vendor a reason to want those twenty seconds gone.
Worse, a call that resolves nothing is billed on the same terms as one that does. The customer who calls again the next day is billed again. A unit that measures duration cannot, in principle, distinguish between a call that was completed and one that merely ended.
It is the same weakness that makes answered-call rates look so good in reports: both count activity. The number that actually says whether something was resolved is how many people call back about the same thing within a day – and that is not a number any vendor invoices against.
