Where did you buy the phone?
HAve you gone to settings/general/restrictions is facetime on there?
The governments in some middle eastern countries have banned Facetime and it is disabled on iphones purchased in those countries. The countries include KAS, UAE and others. There is no way to get Facetime on such phones (for example it cannot be downloaded and installed) and taking the phone to another country does not cause Facetime to reappear on such phones. In support.apple.com/kb/ts3367 it says “Note: FaceTime may not be available, or may become unavailable, on devices purchased or used in certain countries, including Saudi Arabia and the United Arab Emirates. Check your device's region of purchase for more information.”