Apple just released iOS 4.0.1 for iPhone 4, iPhone 3GS and iPhone 3G. This software update is said to fix the antenna issue which is supposedly related to a bad math formula regarding the the display of the iPhone’s service signal bars.
At the same time, Apple also updated iOS 3.2.1 for iPad.
As always when a new firmware comes out, it is highly recommended you DO NOT update if you rely on a jailbreak or unlock. Updating your device might prevent you from jailbreaking or unlocking it in the future.
You can download the new firmwares from our iPhone downloads section.