It looks like Apple has released a new iPhone 3.1.3 update for iPhone, iPhone 3G, and iPhone 3GS users. This new update includes the following fixes:

• Improves accuracy of reported battery level on iPhone 3GS
• Resolves third-party application crashes
• Fixes bugs with Japanese keyboard

You can either download the iPhone 3.1.3 update through iTunes, or you can also download it directly from the iPhone userbar.