Are you placing calls through the manager interface?
You just have to watch the events coming from the Asterisk box. It is in all sent in plain text via a TCP connection and is pretty 'human friendly' to read. So you just need to parse the activity to get in specific information you want.
Here's a link to what many of the events look like,
http://www.voip-info.org/wiki/view/asterisk+manager+eventsJust off the top you are likely going to be looking for callerID information from a newchannel event - fired when a call comes in. Then watching for the internal extension that it gets connected to for the callerID to display.
If you can relay some more information about what you have tried I'm sure we can get you up to speed easily.