Hi Paul,
You did not gave us much technical details about your project.
Read something about Caller ID in ETS 300 778-1, -2, if you are from Europe, or Bellcore Publications.
If this could encourage you, I made something in this domain: sending the caller ID between two telephone exchanges (using CCITT MF-R2 signaling system), and also, sending Caller ID from the telephone exchange to the subscriber's telephone set (using FSK). Both applications were made with AT89C52.
Gabi