Trying to activate a iphone 4 I bought used. Upon online activation, it asks for a serial number. I enter the serial number and it is not the correct format. Someone told me to find the HEX or Dex number which I guess, is the Identifer (UDID). Through Itunes I found the UDID, it is a 40 digit number. Is this the same as the serial 11 digit number found on the iphone itself, through Settings..General..About?