In just a little under a month after iPhone OS 3.1 was released, Apple has just released an update for the iPhone OS, upgrading it to 3.1.2. This update fixes the widely reported issue where the iPhone would not wake from sleep, and also fixes an issue involving video playback and cellular service. This update is available for the original iPhone, iPhone 3G and iPhone 3GS, and the iPod touch.
Update: There's also an carrier settings update (which does not seem to do anything) and an update to the iPhone SDK on the iPhone Dev Center.
Thanks to everyone who sent this in!