Since I've updated my 3G iPhone to 3.1, it will become unresponsive after ~4-5 hours. It looks like it's off, but it's not. None of the buttons do anything that I can see. The only way I can get a screen back is to do a hard reset (Power + Home). Has anyone else had this problem? What can I do to fix it?

I've had it 3 happen 3 times already. Very annoying. Apparently, the Discussions forum on Apple.com also shows lots of people are having the same problem. One guy said he did a restore and that fixed it for him, which I haven't tried yet because many others also tried that and it didn't help. A few others have said turning off WIFI fixes it for them, so I'm going to try that today.

Another thing I've noticed is that now, when I plug in my iPhone to my Macbook Pro, iTunes 9 does not launch. It used to before the update.

** Further update and possible solution **

I left my iPhone plugged into my Macbook Pro yesterday while at work, and didn't use it much throughout the day. I noticed it didn't lock up once. I suspect this was because it was connected to a power source. I continued to use my iPhone with no problem yesterday and today. Still no lockups as of now.

I personally think this was Spotlight and/or Genius "doing it's thing" from a new install. Kinda like an OS upgrade on your Mac... Spotlight has to rebuild itself and those first couple of hours can be kinda sluggish. This would be even more so on the iPhone where processing power is limited, and I'm sure the processor is clocked down a bit while on battery power, which would further amplify the problem.

Again, just my guess. My iPhone is working fine now.

** Final Solution **

Update to 3.1.2. Problem solved.