I was at a clients site today activating a new switch for printers and other "low speed" devices. While I was there they had an interesting issue with the Cisco IP phones. I'm not their "Cisco Phone Guy" so this was not a system I configured. It's actually the first Cisco VOIP equipment I've touched in years.

The issue was, randomly the IP phones would change their extension number and what user was logged in. I actually watched one phone for about 10 minutes. It would register as one extension, then 30 seconds later re register as someone else.

I managed to log into their Call Manager System ( both GUI and telnet) it APPEARS that each phone MAC is set for only one extension #. So I was a little confused on the issue.

Eventually I gave the 2581 ISR a reload and everything came back up as it should.

Has anyone seen this issue before? I can PM a running config if you have any insight.

As I said, not my phone installation. I'm just interested in the solutions.