Cisco 7970 phone to work as pbx on a pfsense box

I need support configuring a Cisco 7970 to work on a PBX hosted on PfSense. The package installed is Freeswitch, but asterisk can be used too. The phone has been already upgraded with a sip firmwire, and the phone has been configured with a SEP Conf xnl file. At present it is unable to register with the package hosted on the PF Sense box I am very busy and could do with some help getting this to work. Its a configuration issue and need someone to talk me through the process of getting the equipment to talk to each other. On completion I will need to be clear on how i configure a System by myself. I can work with remote access and Skype to complete this task.