The problem is, that there are regulations in the country where the iPhone has been sold, i.e. where it is supposed to be used. If you buy an iPhone from a country, where FaceTime is an option by the carrier, you will be able to use FaceTime in the UAE, at least via Wi-Fi.
The iOS firmware is also country specific, meaning, some features might not be available for or in another country, because the carrier does not support this, or due to other regulations, that Apple has to follow in these countries.
Check this article about it:
Here's some info from Apple as well:
- Personal Hotspot3
- Wi-Fi Calling
FaceTime isn't available in the United Arab Emirates.
- The carrier, not Apple, provides technical support for iPhone in this country or region.
- You need iOS 6 or later to use FaceTime over Cellular. You might notice decreased performance on some carriers while using FaceTime over Cellular on 2G networks.
- Might include an additional fee or requirement. Contact the carrier for more information.
- Carrier doesn't support MMS.
- VoLTE is available only on iPhone 6 or later.
FaceTime may be unavailable if your device originates from this country or region and becomes unlocked or is used in another country or region.
FaceTime isn't available in all countries or regions.
copied from: Wireless carrier support and features for iPhone in the Middle East - Apple Support