I am getting fed up with the iPhone 4 now, I am on my third one, all directly supplied by Apple and each one was brand new and sealed. First one would reboot randomly as and when it felt like it, even when in use, second one did the same. My third one just received a text message, lit up and started the tone, then the screen went black, when I pressed the home button it lit up again but the tone came out all garbled and messed up. Also there are occasional freezes, one froze the camera before the shutter (on the screen) opened and took a few minutes to continue operation.
This has happened on iOS4, 4.0.1, 4.0.2, 4.1. Not upgraded to 4.2 yet as waiting for jailbreak. Restoring to a newly downloaded clean iOS does not remedy.