Pull up your address book, locate a recipient that you know has an iPhone or an iPad, scroll down to the bottom and tap on 'Facetime', if it is present. If not, update the OS, if possible.
At present the FaceTime feature will only let you make video calls over a wifi connection, although Apple is working with mobile networks to activate FaceTime over 3G. Once the app has opened, you will need to sign in with an Apple ID. This will be the Apple ID/email address that people will be able to use to call you on. If you do not have an Apple ID simply tap Create Account. For more information visit at Offshore Apple iPad App Development Company - iPad Applications Developer