There are all sorts of Android skins to make an Android phone look like an iOS iPhone. That does not mean they are running iOS. As already mentioned, the only way to even get iOS is to buy an iOS device.
As for the illegal issue - iOS is Apple's proprietary software. They license it to run on their devices. They do not license it to run on other manufacturers devices. Also, since Apple designs the actual chips in their devices, it has thus far proven impossible to install iOS on non-Apple hardware. The various claims and videos of people doing it have regularly been shown to be false and faked.
There are many skins and launchers for Android that will attemp to make your phone look and behave like an iPhone - many are actually pretty flaky and unreliable though.