At last, Apple has released a much-needed patch: iPhone OS 3.1.2 is out and it solves the sleep issue--in which the iPhone refused to wake up--brought in by the previous version. There are other fixes too:
• 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
It weighs 241.7MB. Go get it in iTunes. After the update--which is also available for the iPod Touch--you will be able to update to AT&T Carrier Settings 5.6.
-- Post From My iPhone3g