I came across this problem where the phone just keeps freezing and rebooting everytime I try to get buy the unlock screen. I found an unconventional solution to this problem but before going through this make sure that your problem is sound related (try pressing the volume button if phone freezes then my solution will work). You have to be persistant with it as it could take several attempts before working but keep going.
Try my jacksucker solution and force reboot by holding the home and power for about 15 sec (phone will go off and switch back on with apple logo). If this doesnt work do the fix from the begining by starting here.
Please let me know if this worked for you by commenting and please feel free to donate a few bucks or click on an ad from this page.