If it originated from the Middle East, it'll fall into one of three categories:
1. If it originated from Egypt, Qatar, Oman, Jordan, Lebanon, Bahrain, or Kuwait, it won’t have FaceTime outside the Middle East.
2. If it originated from Saudi Arabia or the United Arab Emirates, it’ll only have FaceTime in the countries listed under #1 or with a new SIM card or carrier update.
3. If it originated from Israel, it’ll have FaceTime worldwide.
For a country not listed, choose Settings, General, and About. If the letters just before the slash are AB or AE, it falls into #1; it isn’t clear which category those with AH fall into. If they’re different, it falls into #3; for reference, one originating from Israel will have HB there.
If it originated from outside the Middle East(except for Pakistan), or a country listed in #3, check the device’s restrictions, search for it, or redownload it from the iTunes App Store. Pakistan falls into #2.