Definition
A toll-free number is a phone number, such as an 800 or 833 number, where the called party pays for the call instead of the caller. In North America it uses one of seven special prefixes.
How toll-free numbers work
In the North American numbering plan, toll-free numbers start with 800, 833, 844, 855, 866, 877 or 888. The FCC’s guide lists these seven codes and notes that they are not interchangeable: a number under one prefix can belong to a different subscriber than the same digits under another.
Numbers are assigned by Responsible Organizations, called RespOrgs, which are certified by Somos, the administrator of the toll-free database. The FCC also bars a RespOrg from reserving a number without an actual subscriber. You normally rent a toll-free number from a carrier or platform rather than dealing with a RespOrg yourself.
When someone dials, the call reaches a lookup in the toll-free database, which names the carrier and route for that number. The call then continues like any other, for example to your SIP trunk. The caller pays nothing for it. You pay for the inbound minutes, usually at your carrier’s toll-free rate.
Why it matters for voice agents
A toll-free number is a common front door for support and for service lines that customers expect to reach at no charge. For a voice agent, the practical effects are about cost and capacity.
Every minute the agent spends on the line is billed to you, twice: once by the carrier for the toll-free minutes, and once by the agent platform. A long call, or a caller who leaves the line open, costs the same as a call on a regular DID, plus the toll-free rate.
Capacity needs thought too, because a publicly printed line can see bursts of calls that exceed your concurrent call limit.
Check with your carrier whether callers outside North America can reach the number, since international access varies.
Example
An illustrative setup: a retailer prints one 800 number on receipts. The agent answers every inbound call on it, handles order status, and transfers anything else to a person during staffed hours.