Blackberry cell phone locked up (by 3 users)

two things you could try: unplug the blackberry from the ac and remove the battery for a hour to discharge it. then place the battery back in and see what happens, if that doesn't fix it, see if you can reload the handheld software on the device. (if not aware on how to do this, your provider can help you with it). If that still doesn't fix it, then you have to replace the device.