This update contains improvements and bug fixes, including:
Fixes a bug that could allow someone to bypass the passcode and access the Phone app
Improvements to Maps in Japan
For information on the security content of this update, please visit this website: http://support.apple.com/kb/HT1222.
iOS: How to update your iPhone, iPad or iPod touch article http://support.apple.com/kb/HT4623.
Available via iTunes