The long expected iPhone 3.0.1 update being pushed out via iTunes fixes a much reported vulnerability.
The update specifically addresses the much reported SMS device control and exploit that has been blown into a source of hysteria across media outlets.
Update: It should be noted that this update will cause jailbroken iPhones to revert back to their default state according to a spate of reports received as well as independent confirmation.
Also, this of course will remove any unlocks on your phone. Wait for PwnageTool and redsn0w to be updated if you want to keep your jailbreaks and/or unlocks.