You can also use the Find Me feature associated with the Technician's mailbox. It's very easy to call in and change the Find Me phone number. No ITP Phone, SoftPhone or software required, just dial into the mailbox.

This would be you're easiest option and probably doesn't require any reprogramming. The caller chooses option two to reach the tech. If he's at his desk, he gets the call. If he steps away, he turns on Find Me and the call goes to his cell phone.