Hi Alyn,
We had this trouble a few times with 7.x Firmware for 7941's and 7961's. This never happened again with 8.x Firmware;
bugid=CSCsc99161
Symptom:
Rarely a 7970 IP phone will get into a state where the speaker, headset, handset, or line buttons will not work to take the phone offhook. In this state the only way to go offhook will be to use the softkeys.
Conditions:
This has been seen in various Skinny phone loads up to and including 7.0(2)SR1. It is not dependant on CallManager version.
Workaround:
A simple IP phone reset will recover the phone.
Further Problem Description:
This problem can occur on Cisco IP Phone 7906/7911/7941/7961/7970/7971 independent of phone protocol (SCCP, SIP) and CallManager version.
Firmware 8.0(4)SR1 or later can resolve this problem.
Hope this helps!
Rob