iPhone 3Gs battery problem

Hello,

I put my phone on charge the other day, ive had the phone approx one year and the battery has always been fine.

I plugged it in and it made the usual sound and the usual screen, when i glanced at it a moment later the apple logo appeared (the turning on logo even though it was already turned on) and i picked the phone up to find it was VERY hot almost to hot to hold. The phone was now not responding to the power button so i took it off charge and it stayed like this for about 20mins. It now will not charge or turn on by any method. I have tried the cable with an ipod touch and that was fine. What should i do? I bought the phone in january so the 1 year warranty has just run out.

also i cant seem to find an imei number there isnt one on the back or on the sim tray?

Thanks in advance for any advice.