I bought my iphone 3gs in the states. And I jailbreak it because I'm not an AT&T customer. One day the phone just put itself into the DFU mode! I didn't do anything. So it's black screen. I tried to restore my iphone but I can't. During the restore process, my phone will be white screen for a while and then turn back to black screen again. And then itunes will show the message that my iphone can't be restored. Then I get the error code, sometimes it's 1618, sometimes it's 28 and it even shows 20000 for a few times. But mostly 28, I couldn't find 1618 and 20000 in apple online manual. I check the manual and it seems like 28 represent there's an hardware issue...
iphone 3gs, iOS 4, I'm using iOS 4.0.1 on my iphone
Ohh...... what if I take it to Apple store and ask them to fix my iPhone, will they be able to fix it??
Unlikely, The warrantee for US iPhones is valid in only the US, and not for jailbroken ones anywhere.
If it's just a software problem, any fix would probable involve a restore which would install 4.1, so it would relock to AT&T.
If you know someone in the US, they could try an Apple store there. If it's a hardware problem, they might replace it, but the replacement would be locked to AT&T.