Below you will find the schematic and explanation of a Caller ID interface with a serial port (from a PC for example).
http://matthieu.benoit.free.fr/cidfr.htm
This project describes the development of a system to interface the telephone line with a microcontroller. Using this interface any device can be controlled using a telephone or cell phone. The system involves the use of DTMF tones commonly used in telephone networks.
http://www.uchobby.com/index.php/2007/09/30/phone-to-microcontroller-interfacing-with-dtmf/
http://www.epl.co.uk/info3.htm
http://www.boondog.com//tutorials/dtmf/dtmf.htm
based on Basic Stamp microcontroller, it hears touchtones and displays them as telephone numbers.
http://www.bobblick.com/techref/projects/tonedec/tonedec.html