Maybe I'm being a total muppet but this is a new one to me. I have done a lot of SIM swapping in my time but have never had this before. On my recently acquired unlocked G1 I am using my Orange 3G SIM. I get a great 3G connection, can receive incoming calls, can send and receive SMS, update network settings, etc., yet cannot make calls. If I put my T-Mobile PAYG SIM in it works fine. If I put my Orange 3G SIM in anything else it works fine. Can anyone shed any light on this? BTW, before you ask, I've done a soft-reset, hard-reset and 'reset to factory defaults' from the Settings menu but nothing has made any difference.
Your help would be much appreciated.