Local phone numbers in the US and Canada follow a specific format. Let’s look at an example phone number: 1415906XXXX. This number can be broken down into four parts:
- 1: Represents the country dialing code
- 415: Numbering plan area code of the phone number (NPA)
- 906: Exchange code (NXX)
- XXXX: Line number or subscriber number
All local phone numbers in the US and Canada follow this notation: (1) NPA NXX <Line>.
Each of these NPANXX combinations is assigned to a rate center that defines the boundaries of local calling and subsequent billing. Calls between phone numbers belonging to the same rate center are considered local calls and are subject to local calling rates, whereas calls between different rate centers might be subject to long distance calling rates.
Some important points to note here:
- Each rate center has multiple NPANXX combinations associated with it.
- Each NPANXX is uniquely associated with one rate center.
- A single NPA might be mapped to multiple rate centers, so using numbers with the same NPA does not guarantee local calling rates.
We at Plivo try to provide a variety of phone numbers to our customers, but we cannot guarantee the availability of all NPANXXs. A local_calling_area filter in our phone number search API lets users search for phone numbers that match the local calling requirement for a particular NPANXX prefix.