Asterisk Cisco 7911G extension

Force the phone to update its firmware:

1. Power off the phone.
2. Hold down #.
3. Power on the phone while continuing to hold #.
4. Release # when the handset indicator starts blinking.
5. Enter the code: 349167285*0# or 123456789*0#.

Links:

Cisco 7911 Background and RingTones settings https://www.voip-info.org/asterisk-phone-cisco-79x1-xml-configuration-files-for-sip/