Interval between checking for signal from a tower?

I live in an area where at&t has weaker coverage so there is no coverage inside the building. The phone often goes between one bar and "No Service".

If I am going out I'll check after driving a few miles (around 5 - 10 minutes) into an area with much stronger coverage, but find that the phone still shows No Service. A phone restart will cause it to search for service and will pick up a full 5 bars with full edge.

Not jailbroken, not unlocked, 3G iPhone with the 2.0 software. 3G is disabled on the phone. The first generation iPhone with 1.1.4 did not have any similar problems.

Any similar issues for any of you?