Help need, situation iphone 3g - 2 months old, running ver 2.21. With the sim in another device ie, phone I can send & recieve calls and txts, I can also send & recieve data when the sim is inserted into a datacard, so sim is OK

When i try to use the sim in the iphone - i can connect to the internet OK ie send & recieve data, I can send and recieve txts however incoming txt's do not alert - no sound

When I try and ring out I get call failed, incoming calls do not ring however the caller hears a ringing tone, The phone shows incoming caller and displays who is calling however within a few seconds it goes call failed and show missed call.

Call forwardng is OFF,  Call waiting is OFF, TTY is OFF, Location is ON, Ringer volume MAX, Enable 3G is ON, data roaming is ON, feild test shows -79db

So.... what can be the problem