A:AnswerThis is not a handset with an answering system built in to itself. This is a replacement handset that can be used with an additional purchase of the AT&T Cordless Answering Phone System. This handset does have caller ID, Directory for Contacts as well as the ability to review your messages from your main answering system unit remotely. Hope this helps.
A:AnswerYes, the quick start and the User's manual shows it is compatible.
EL50003 / EL50013 is for use with AT&T models:
EL51103 / EL51203 / EL52103
EL52113 / EL52203 / EL52213
EL52253 / EL52303 / EL52313
EL52333 / EL52353 / EL52403
EL52503