I called my girlfriend on my iPhone 4 and she didn't answer so hung up and put it back on standby.

Then the phone started vibrating continuously for a minute and a half, maybe 2 minutes, and now it's completely dead. I've tried holding every combination of buttons and charging/syncing it, but nothing.

I'm going to take it to an Apple store tomorrow with my original iPhone 4 receipt and my O2 airtime receipt to see what they can do.

Has anyone else had this problem, and if so, how was it resolved?

When it happened to my sons,he held down the home button and the power button for about 10 to 15 seconds the phone then closed down and then restarted and its been ok since

You're a star - it worked! Thanks very much!

He got the info from Google ,

it seems a common problem