@bjkhan
First of all, EDGE/GPRS and 3G/HSDPA are 2 different radio band. The reason why you have signal on EDGE/GPRS and not 3G in certain area is due to network coverage and not entirely the phone. The old network (EDGE/GPRS) is using GSM (which have a wider coverage) and 3G's on UMTS (if not mistaken). 3G is relatively new hence the poor coverage. Maybe maxis was doing some maintenance on the tower nearby you that time. I once experience this with Digi, the signal dropped where last time it was a full bar. A quick check with digi shoes that they are doing some work to the tower.

Last time the 1st gen iPhone had a problem with maxis network (the early iPhone adopters will remember this). Only after a few months maxis patched their towers to support iPhone. Other telcos are not having the problem.

Why i said its not entirely caused by iPhone? This is because the iPhone 3G baseband (the part that controls the phone signal) is known to have a problem latching on to the 3G network. People in the US is still complaining about 3G blind spot where other phones does not experience it. Just hope apple will patched this and resolve issues regarding 3G signal. One more thing, the iPhone should drop its 3G connection and switch to GSM signal once the signal strength weaken. I dont know why yours did not automatically swith the network. Like i said, maybe its maxis doing maintenance and the iPhone still detect a strong 3G signal. Thts why it did not switch network.

What you can do is just give maxis a ring and ask if they are doing some tower maintenance or something near your office.