Iphone 3G shows 'no service' eversince I came back from Malaysia

I'm using Iphone 3g for a year exactly and have no problems at all until recently I went to Malaysia. it says 'no service' where the carrier name supposed to be. so I assume its because since I'm out of the country, Singtel can't get coverage where Im at. I returned to Singapore 2 days later and still it says 'no service'. I tried doing all hard reset, clean restore, wipe everything out, tried toggling the airplane mode, still no improvement.. I thought maybe my line got cut and called Singtel but they assured me that the line is working perfectly fine. The singtel iphone tech support guy tried advising me to do the network reset but still no use. I doubt it has anything to do with my sim card as I tried using it on other nokia phones and I can get full signal. I'm sure its the phone with the problem. I can't get a replacement phone from Apple as my 1 year warranty ended last month! why is this happening! feels like iphones go into self destruct mode just when the warranty finish so we have to fork out money in repairs. anyone experiencing the same problem? it's been 5 days.