First you will need the SIP firmware for the phone, as they are supplied with SCCP firmware.
You can download a package I have built here. You can also download the latest version from the Cisco website, they are free and available with a standard Cisco website account.
You will also need a TFTP server that the phone can connect to, and if you do not force a TFTP server address into the phone your DHCP server will need to pass option 66 with the TFTP server IP address. Windows 2008 R2 DHCP options has this as 066 “Boot Server Host Name”.
Extract the zip file into your TFTP root directory and then edit the SEP#######.cnf.xml file, search for the word “FIXME” and read around those lines to fix and replace for your setup. Then rename the file to be the MAC address of the phone. Replace ######### with the MAC as the sample file has already.
You may wish to also edit the dialplan.xml file and set your area codes and other stuff.
The phone will boot up on the network, grab an IP address from your DHCP server, pull the TFTP server address from the DHCP options and then contact the TFTP server. It will pull the SEP#######.cnf.xml file that responds to the phones MAC address. After some reboots and firmware changes it should register to your SIP provider.
I have this all working for voip.ms. If you are behind a firewall you may have issues with NAT. I am using pfSense and have no issues. The phone has NAT turned off (in the config already) and voip.ms settings for the sub-account I am using has NAT set to ‘yes’.
Lots of info was found on the voip-info website.