From the below quote from cisco to convert sip to sccp 7960, where cani find and edit the file OS79XX.TXT?
SIP Images 4.x/Earlier to SCCP Images 6.x/Later
If your current SIP images is 4.x or earlier, complete these steps in order to convert to the desired SCCP images 6.x or later:
Complete these steps in order to convert to the 6.3 image first:
Copy the desired binary image from Cisco.com to the root directory of the TFTP server.
Open the OS79XX.TXT file with a text editor and edit the file to include the desired image.
Specify the desired image in the protocol configuration files.
Reset each phone.