This functionality allows incoming calls from your land-line (PSTN) connected to the OBi110 to be answered by Auto Attendant, and thus allowing the caller to make a new call via ITSP (for lower termination rate).
Make certain that:
a. PSTN land-line has a callerID function (many US telco providers require extra monthly charge just for this)
b. In the US, enter the callerID format as 10 digit number (without the "1" in front of it). E.g.: 4085551212 would be what you enter into the field, not 14085551212.