More about Calling Line ID and Calling Party Name

CallerID, as it is typically referred to, actually consists of two user-facing identifiable pieces of information: - A phone number (typically referred to as CLID or calling line ID) - Calling party name (typically referred to as CNAM) which can be up to 15 characters in length.

When a call is made, the CLID (phone number) is routed to the destination's carrier (also known as the terminating carrier). The CNAM info for the call may or may not be routed with the call as this depends on how the country has implemented CNAM (if at all). The reliability of CNAM delivery with the call varies depending on the country and carriers which handle the call either as an intermediary and/or a terminating carrier.

CLID & CNAM transmission is the responsibility of the terminating carrier insofar as the terminating carrier must support CLID & CNAM functionality as well as provide up to date records for both values. Microsoft reliably provides CLID values when originating calls, but those values may not be kept intact once they pass through an intermediary carrier or the terminating carrier. Unfortunately, in the event the CLID value is changed, omitted or truncated by the intermediary or terminating carrier, Microsoft has little to no recourse in correcting such problems in the public telephone network.

Inconsistencies in CNAM can be caused by delays in intermediate or terminating carriers refreshing CNAM info in authoritative databases as in the case of the United States. In countries where there is no authoritative database for CNAM, individual carrier practices can also cause problems with CNAM information arriving in tact with the call. Microsoft currently does not support originating CNAM information in countries other than the United States."