Out of the 200+ features of iOS 5, Apple’s video calling feature wasn’t included in the latest mobile operating system.
However, there is one way in which you could get FaceTime on your device, even in iOS 5.
The app is exclusively designed for mobile devices running in iOS with a forward-facing camera but by hacking one of the system files FaceTime can be installed on iPhone 4 as well.
Here are the steps to follow: first, you have to download iFile for iPhone from Cydia or iExplorer for Mac and Windows. Then you browse to /System/Library/CoreServices/SpringBoard.app/.
Open the file named N90AP.plist and add in 3Gvenice under capabilities. Next you click save and you’re done.
FaceTime works by connecting an iPhone 4 or newer iPhone, an iPod touch, an iPad 2, or a computer with Mac OS X to another similar device.