Apple has quietly release iPhone OS 3.0.1 today to address the SMS security vulnerability issue Users with iPhone are strongly urged to update their devices through iTune.

According to the Engadget, the update weighs in hefty size at close to 300MB. The site also has a quote from Apple's rep Tom Neumayr about the vulnerability:

We appreciate the information provided to us about SMS vulnerabilities which affect several mobile phone platforms. This morning, less than 24 hours after a demonstration of this exploit, we've issued a free software update that eliminates the vulnerability from the iPhone. Contrary to what's been reported, no one has been able to take control of the iPhone to gain access to personal information using this exploit.

Source: Apple