Blackberry Curve 8330
This just happened to me. I ran my mouth on the phone and the battery life went down to 0%. It wasn't until I looked in the OPTIONS then STATUS section of my BB that I found that it was in RADIO OFF status.
So all I did to solve this was take the battery out while the phone was turned on and then count to 10 and put the battery back in. Then when I turned it back on, the hourglass showed up and it took awhile but it finally loaded my applications again. I waited a minute after that and all of my emails and text messages dropped in.
When I looked in my OPTIONS under STATUS, the signal no longer said RADIO OFF. Instead it showed that I had dBM's coming through and I was able to make a call. IF you get to this point and it doesn't work and you're on Verizon Wireless you might have to also call the *228 reprogramming number from your cell phone so that they can reprogram your phone over the air.
I hope this helps those who need it!