Although SIP phones will allow you to specify the name of the caller (also known as CNAM) as well as the calling number (also known as CLI), caller name information is not passed to the last mile carrier, because it is not supported by the TDM switches used by landline carriers. To the contrary, the called party’s LEC (local exchange carrier) is in control of the caller name and CLI that its subscribers see.
When caller name is displayed to the recipient, it is because the last mile carrier subscribes to a caller name database, also known as CNAM. This database is unrelated to the caller name that may have been entered into the caller’s SIP phone. Therefore, the caller name seen by the call recipient may be completely different than the name entered in the SIP phone. Or, it may not be shown at all, if the last mile carrier does not subscribe to a CNAM service.
As a point of reference, most U.S. mobile carriers do not use the CNAM database. As a result, mobile phone users will rarely see a name on inbound calls, unless the caller is in the mobile phone’s address book.
