I've got a 2.1 FW 2G iphone with T-Mobile.
Throughout the day around 3-5 times when I go to unlock my phone the clock will display the correct time and then in a flash it will reverse like around 30 minutes and the wrong time will stay until I reboot. So then I have to reboot my phone to get the correct time again. It's really annoying and I was late 30 minutes to work yesterday!

Needless to say, I don't trust my time on the phone anymore.
ANyone else with a similar problem or any idea what the problem could be?