Hello,
I am using iPhone on 1.1.2 on the Telstra network in Australia (have only been using it 4 days). Everything was fine for 2 days, then for the first time I accessed Edge to download a couple of emails. Don't know why but after this I stopped being able to send SMSes. It would say "Error Sending Message", then "No Service" and then "No Sim Card Installed". Sim texted fine from my old phone. I thought it was message center number and was about to manually enter it with the hack key, then I had a re-think and went to Settings / Carrier which, on the main Settings page, read "Telstra mobile". But then I selected "Carrier" to go into that menu, I found "Automatic" was ticked. (Maybe this happened when I accessed Edge? Who knows?) I manually selected "Telstra mobile". Turned the phone off and on and everything has been happy since. So far. Just a thought, worked for me. Now my iPhone and I are in love again!