iOS 4.0.2 is Available for iPhone 4/3G/3GS and the iPad too

The iOS 4.0.2 Software Update includes a new security update and the iOS 4.0.1 improvement to the signal strength formula for iPhone 4, iPhone 3GS, and iPhone 3G. The real signal strength remains the same, but the bars on iPhone will indicate it more precisely.

Compatibility

iOS 4 works with iPhone 4, iPhone 3GS, and iPhone 3G. Not all features are compatible with all devices