This past week my iPhone (original, 3 yrs old) suddenly refused to turn off. I tried a restore, tried taking it in to a "genius" with no success. My son sent me a phone to use in the interim, so I took out the SIM chip to put in the new phone. I found a big wad of lint alongside the SIM. When I cleaned it out and put the SIM chip back in, problem solved. When in doubt, clean it out!