For all SCCP firmware upgrades from firmware release versions earlier than
8.3(3) to version 8.5(3) or greater, you must first upgrade your firmware to version
8.5(2). Once you have upgraded to version 8.5(2), you can upgrade your IP Phone to version
8.5(3) or later.
For more information we can also check the Cisco Unified IP Phone Release Notes for
Firmware Release 8.5(3) at the below URL:
