As mentioned in the release note of the update, iPhone OS 3.1.2 fixes three important bugs
  • Resolves sporadic issue that may cause iPhone to not wake from sleep
  • Resolves intermittent issue that may interrupt cellular network services until restart
  • Fixes bug that could cause occasional crash during video streaming

The update is already live. If you’re not using jailbroken iPhone, simply plug your iPhone to computer and upgrade it via iTunes. Once finished, your iPhone will be automatically restarted. That’s it. For AT&T user, after the OS upgrade, you’ll also be prompted to update the carrier file to v5.6.

For jailbroken iPhone user or those who intends to jailbreak their iPhone, please hold off the upgrade. For now, you should not upgrade your iPhone directly in iTunes to iPhone OS 3.1.2. Otherwise, your iPhone may not be jailbroken again. The iPhone Dev team also mentioned in its blog not to upgrade to the latest version:

  • PwnageTool and redsn0w are not yet compatible with 3.1.2
  • There is no estimated release time for compatible tools (please don’t bug us about this).

So jailbreaker, remember to stay away from the upgrade. Other that the above bugs, Apple doesn’t mention anything bug fixes about battery performance. Despite of that, if you have installed the update, be sure to let us know if you find any improvement regarding the battery life.