I've had this phone since December 2008 and have had it jailbroken for about a year now. I've never had any real problems with the phone, I did drop it and destroyed the digitizer but replaced it myself. A couple of weeks ago I kept getting messages that this device is not supported and you may hear feedback. There was nothing plugged into the phone, it was working fine other than that message. Later on that night the phone wouldn't make any sounds whether it be out of the speakers or the phone speaker. It seemed as if something was in the earphone jack and the phone was trying to output to it. About an hour of trying to figure out what was wrong it started working but then it started saying that the charging device was not supported. I wasn't trying to charge it... but when I eventually had to charge it it wouldn't charge. My phone is now completely dead, won't charge, the phone won't even recognize a charger connected to it. Any ideas?
Sounds like it could either be a battery/charger issue or something more serious. If you know anyone who also has the same phone, try using their charger/battery. If that gets it going you'll probably want to buy a new battery/charger. If that option doesn't work and based upon the messages you were getting, it sounds like it could be an internal issue, i.e. overheating may have damaged something, etc... In that case you may want to take it in to be repaired or perhaps buy a new phone.