For most enterprises still reliant on the 7975G, the least-bad option is to if it is stable, but accelerate the hardware replacement project.
For those connecting to non-CUCM platforms like FreePBX, remember to update your SEP .cnf.xml with the correct tag to trigger the update. cmterm-7975-sip.9-4-2sr4
This release is a Maintenance Release for Cisco Unified IP Phones in the 7900 series. It is typically deployed as a .cop.sgn file (Cisco Option Package) on a Cisco Unified Communications Manager (CUCM) to provide updated phone software to end-user devices. Key Features and Use Cases Decoding cmterm-7975-sip