I'm 99% sure its RMA time for these phones. This is most likely a problem with the Hookswitch. After deploying Cisco IP Phones for the last few years we (and many others) have found this to be the most common hardware problem.
There is a "Best Practice" for cleaning the Hookswitch contacts (link below) that does work on occasion. Usually the phone has to be replaced/RMA'd.
Best?? Practices for Cleaning and Troubleshooting Cisco IP Phone Hookswitch
There was also a problem with the 7.2 phone firmware that caused similar looking symptoms for the 3rd generation phones like the 7970/7961/7941. This could be rectified in the short term by booting the phone. If your issue can be fixed by resetting the phone and you are running 7.2 firmware, let me know and I will find you the Bug.
SIP traces provide key information in troubleshooting SIP Trunks, SIP
endpoints and other SIP related issues. Even though these traces are in
clear text, these texts can be gibberish unless you understand fully
what they mean. This document attempts to br...
Please find the attached HTML document, download and open it on your PC.
This provides an easy to use form where you simply answer a few
questions and it will render the proper jabber-config.xml file for you
to copy/paste. There is built in logic to verif...
CUCM Database Replication is an area in which Cisco customers and
partners have asked for more in-depth training in being able to properly
assess a replication problem and potentially resolve an issue without
involving TAC. This document discusses the bas...