Most carriers in the United States and in all of Canada use flat-rate billing for local calls, which incur no per-call cost to residential subscribers.
As regulators in North America had long allowed long-distance calling to be priced artificially high in return for artificially low rates for local service, subscribers tended to make toll calls rarely and to keep them deliberately brief.
The billing of calls was not itemized and the expensive fixed-rate line was only within financial reach of large corporations and government agencies.
Typically, a service provider offered a variety of zones, each costing more than the smaller ones, but adding progressively larger areas from which calls would be accepted for a customer.
Prior to the toll-free long distance market was opened to competition after 1986, a customer may have had a multi-carrier toll free number assigned by the Local Exchange Company for intrastate callers and an order placed with a long distance company for interstate callers.
A RespOrg system was implemented in 1993 to provide toll-free number portability between rival carriers using the SMS/800 database.
Open competition also brought an end to the pattern of long distance subsidizing local service, bringing per-minute charges down to levels where any business could afford to take orders using an 800-number.
SMS/800, Inc. administers this database as the Number Administration and Service Center, as a subcontractor for the Federal Communications Commission (FCC).
These toll-free numbers can normally be called from any telephone in Canada or the U.S., though the owner (and sometimes the provider) can put restrictions on their use.
Calls from pay phones assess the toll-free owner an additional fee in the U.S., as mandated by the FCC.
Examples of these services are the erstwhile MCI Worldphone international calling card and any U.S.-based Internet telephone gateway.
The IXCs generally handle traffic crossing local access and transport area (LATA) boundaries.
When a customer decides to use toll-free service, they assign a Responsible Organization (RespOrg) to own and maintain that number.
SS7 is a digital out-of-band method of transmitting signalling (call control) information in the Public Switched Telephone Network (PSTN).
The subsequent routing of the call may be done in many ways, ranging from simple to complex depending on the needs of the owner of the toll-free number.