Discussions regarding iOS 4.X.X
iOS 4.x: fourth major OS release
iOS 4 was made available to the public for the iPhone and iPod Touch on June 21, 2010. This is the first major iOS release to drop support for some devices. It is also the first major iOS release that iPod Touch users do not have to pay for.
The iPhone 3G and iPod Touch 2nd generation have limited features, while the iPhone 4, iPhone 3GS, iPod Touch 3rd & 4th generation have all features enabled, such as multitasking. The iPhone and iPod Touch 1st generation cannot run iOS 4.0 and above.
iPad compatibility was added with the release of iOS 4.2.1 on November 22, 2010.