The iPhone OS 3.1.3 update is now available via the iTunes store. This a firmware update does very little other than fix some small bugs experienced by users of the 3.1.2 firmware. You can update your phone to the latest firmware simply by connecting it to your computer and letting iTunes download and install it. Direct download links for the update are not yet available, but will be posted once they are. For those of you using jailbroken and/or unlocked phones, do NOT upgrade, as your phone will no longer be unlocked and may become temporarily bricked.