Problem with Cisco phone setup

Hi, I am wondering if anyone might be able to help me out, I have freepbx installed and everything works fine with soft phones I have now purchased a Cisco 7912 phone with sip firmware installed. I have filled in the details in the sip settings part of the phone such as the ip address of the freepbx server, my extenstion number and password etc I can make outbound calls from the phone but no incoming calls or internal calls, also the phone doesn’t seem to be registering in freepbx “0 phones online” is reported on the freepbx system status page, does anyone have any ideas or instructions on what’s needed to get this phone working ?