I had exactly these symptoms using a Samsung Galaxy Ace on Orange in the UK. I couldn't make calls; the "Call Not Sent" message popped up immediately, though it seemed to carry on trying, i.e. if you tried to do something else, it would tell you a call was still in progress. Only powering down would end this process. When I called the mobile from a landline, I'd get ringing tone on the landline, but the mobile didn't react at all. Eventually, it went to voicemail. Also, the Notification bar at the top of the screen glowed bright green, and when powering on, the "Emergency Calls Only" message flashed up briefly top right of screen. I tried powering off and taking out the battery, but it didn't work. However, I tried again some time later, left the battery out for a good 5 minutes, gave the SIM card a bit of a rub on a clean cloth. Re-powered, bingo! Connectivity, all OK so far.