Emergency Call??

For starters, try a reset. To reset the iPhone, press and hold the home and sleep/wake buttons until you see the Apple logo (ignore the slide to power off prompt).

Next step is to perform a Restore via iTunes.

Could also be an issue with your SIM card, so if neither of the above help visit an Apple Store or and AT&T Store for a new one.

I've had this problem too a few times, the latest this morning. Just trying a restore now. Apple Store, where I asked, suggested a SIM problem. Will let you know if I encounter the problem again after that.

Hi all, I am having the this very same problem sometimes, I have a new 3G thats about 1 month old.
the phone works just fine, but sometimes, when i turn it on, its doesnt start up properly, and is just for EMERGENCY calls only. So I shut it off, then turn it back on, and its all fine. Its like nothing was wrong.
I notice this happening about 2 or 3 times in 1 week.
It always seems to start up on the 2nd try OK. Its just a real mystery why it would start in emergency mode only once in a while.
In any case, this should not be happening... I atributed it to bad firmware or something... I did a complete reset of the phone, restoring its firmware fresh and reloaded everything from itunes again, but it didn't help, it still has this proble.
Some days, it just turns on and is OK, and some days, it takes 2 try's to get it to work right.
maybe 2.2.1 firmware is broken?

I have had the problem periodically. Turning the phone off and restarting has always worked -- until this morning. Several restarts have not solved the problem. I get the Emergency Call screen each time. I cannot restore. iTunes cannot connect to the phone -- it suggested a Sim problem. And reset doesn't work either. I guess I'm off to the Apple store unless somebody has another idea.

I had another 3G before this one that was eventually replaced with my current one, and I had a problem with it where it would just turn itself off periodicaly...
I remember an apple tech support person took me through some steps to restore the firmware in the phone....
what he had me do was HOLD the home button in, then plugging the usb cord into the computer, then letting go of the home button once itunes prompted for restore. This prompted iTunes to do a complete phone firmware restore. I don't know if this would help your situation though.

I have been turning the phone on and off all morning to no avail. So when sirFrank posted I decided to try his solution. I turned the phone on and had planned on then plugging it into the computer while holding down home as suggested. No need. When I turned the iPhone on it was working again. There was a window that said phone is activated. I think I might still go to Apple Store and see if there is a way they can check the Sim Card for problems.

Thanks.

Steve

Do you have a passcode lock enabled? If so, seems like the Emergency Call button at the bottom left of the passcode entry screen was tapped.

The same thing happened to me. It is strange. Apple support suggest I restore my itunes.