FaceTime works with Mobily iPhone 4, just don’t upgrade to iOS 4.1
It has been confirmed that FaceTime does work with iPhone 4 units sold by Mobily, there is a catch however.
Right now we recommend that you just wait until it is %100 confirmed why is it happening like that.
Update: Macworld Middle East covered it as well: FaceTime in UAE killed by iOS 4.1 update, users report.
Arabic version of this post on SaudiMac Arabic Edition.