ANI (Automatic Number Identification) is a system utilized by telephone companies to identify the DN (Directory Number) of a calling subscriber.

ANI serves a function similar to Caller-ID, but utilizes different underlying technology. In addition, although Caller-ID can be blocked by prefixing a call with *67, ANI is (usually) impossible to block.

ANI was originally developed for telephone company billing purposes. ANI technology is also now offered to commercial customers who may benefit from knowing who is calling them. In addition, ANI is one of the core technologies behind the 911 emergency service.

ANI data is usually transmitted in-band using multi-frequency (MF) signalling. However, ANI data can also be transmitted seperately if you have an ISDN PRI.