Iphone 3G - Edge and 3G Problems

Hi, sorry for posting here, as this might be a very simple issue to fix. I'm kinda new to the iphone and everything so I hope its ok. And I really appriciate any answers at all =)

I got an Iphone 3g 8gb. The Version says 2.2.1 (5H11) and the Modemfirmware says 02.30.03. It uses a Turbosim card. I think it is a rebel one. As I bought it Im not entirely sure.

It has worked fine up until recently. It froze, so I had to reboot it, and after the reboot, the edge didnt work. Until I switched Data Roaming ON, wich on my brothers iphone is off, and I believe mine was off before that aswell. Anyways, now it worked for about 1 day, and then suddenly it lost all reception. No Sim Card, and No Service. Got home, swapped the sim into another phone, made a call, back into the Iphone and it worked again. Except that the edge or 3g didnt work anymore.

Now, I've tried putting it into another phone, and set manual network, then correct, then onto the internet, then manual network etc several times. But still nothing. I've tried lots of different APN settings, but Im now using the one I used before it stopped working, so that should be ok.

And I've searched the net trying to find out what is wrong, but I cant find any good answers. When I flick the 3G switch on, the reception bars drop to 0 for 3-4 secs, then poops back up, but no 3g or edge icon.

Now this is starting to become a problem.. as Im using the calendar funcion on it while working =)

Any help at all would be very very appriciated !

Thanks in advance =)

-hau

Moved to *sim section