Apple has released a bug fix update to the iPhone OS, version 3.0.1, that fixes a very critical security issue which could allow someone to compromise the device by sending a carefully crafted SMS text message. Plug your iPhone into the Mac or PC you normally sync with, select the iPhone in the devices section of iTunes, then perform an update using the appropriate button on the Summary tab.

NOTE: This does not impact iPod touch users since those devices do not support SMS texting.