If your phone is currently running a version older than 8.3(3), you must first upgrade to an intermediate version (like 8.5(2)) before applying version 9.4(2).
: The .zip extension signifies an "alternate firmware format" intended for manual installation or use with third-party TFTP servers, as opposed to .cop.sgn files used directly by Cisco Unified Communications Manager (CUCM) . Requirements for Use Cisco Unified IP Phone 7975G Firmware Load 9.4(2) SCCP cmterm7975sip942sr4zip upd
: Fixes for memory leaks and registration issues that were common in earlier 9.x SIP loads. How to Access Official downloads require a valid Cisco Service Contract If your phone is currently running a version older than 8