Earlier there was a 3G outage in the Philadelphia, Southern New Jersey area. My iPhone 3GS would simply display "NO SERVICE" unless I turned 3G off. If I turned 3G off, the phone would start using Edge and would work. If I turned 3G back on I got "NO SERVICE" again. This was happening for a number of iPhone users in my office.
Someone else in my office with AT&T has a regular phone that supports 3G and it automatically switched to Edge when it lost 3G service. How come the iPhone doesn't do that?
Mine sometimes has a hard time switching, I know I'm on the other side of the world from you but it's the same idea. Mine goes a bit further and will get stuck in NO SERVICE sometimes all together unless I go in and out of airplane mode and it searches for the network again. So weird!!