Apple has released the 1.1.1 update for the iPhone, which includes the new WiFi Music Store that lets you buy tracks on the go.
If you have Installer.app like Kevin showed us on AOTS yesterday, you'll want to do a restore in iTunes before you upgrade.
If you've unlocked your SIM for use on T-Mobile or internationally... DO NOT UPDATE! There are reports of this process causing problems with unlocked phones.
Hit the jump for the change list:
WARNING: Apple has discovered that some of the unauthorized unlocking programs available on the Internet may cause irreparable damage to the iPhone's software. IF YOU HAVE MODIFIED YOUR iPHONE'S SOFTWARE, APPLYING THIS SOFTWARE UPDATE MAY RESULT IN YOUR iPHONE BECOMING PERMANENTLY INOPERABLE. Making unauthorized modifications to the software on your iPhone violates the iPhone software license agreement, and the inability to use your iPhone due to unauthorized software modifications is not covered under your iPhone's warranty.
iTunes Wi-Fi Music Store
Louder speakerphone and receiver volume
Home Button double-click shortcut to phone favorites or music controls
Space bar double-tap shortcut to intelligently insert period and space
Mail attachments are viewable in portrait and landscape
Stocks and cities in Stocks and Weather can be re-ordered
Apple Bluetooth Headset battery status in the Status Bar
Support for TV Out
Preference to turn off EDGE/GPRS when roaming internationally
New Passcode lock time intervals
Adjustable alert volume