The date isn't set in the phone at all.
I checked in my router (WAG54GP2) and on the status page the time was listed correctly, but on the voice section it is showing as 1/1/2003.
I turned the router off and it corrected itself.
It has just done it again today. Doing a hard reboot doesn't fix it.
Has anyone else seen this? Where does it get the time from?