I'm experiencing this issue also. All received SMS messages have a timestamp that is 5 hours in the past. My outgoing SMS messages seem to have correct timestamps though. This is very strange. I emailed HTC support about it, and all they said was this:
Unfortunately the time stamp on text message is place on the message by your service provider, and there is no setting, on the device, to correct the issue.
However, I know that the previous phone I was using, with the same wireless provider and same sim card, did not have this problem. So I'm sure it's something on the phone that's causing this. Anyone found how to fix this problem?