[asterisk-users] Variable to show caller id for a current call?

[Warren (mailing lists)]

Is there a variable that can be gotten with GetVar to show the callerid 
of the current incoming call in progress at a sip extension?

For instance, a caller from 516-922-9463 calls extension 234.  I would 
like to be able to be able to get back the 516-922-9463 if I pass 234.

Also, can this be done while the extension is ringing?

TIA,
Warren