Hi, from my experience i feel that they are carrier settings, coz i bought an iMac from Dubai, and the facetime icon is there, but when i try to contact people abroad i get a dial tone, connecting, then connection failed. They must be blocking the facetime port from the ISP.
Similarly on the iphone, i have experienced from when i bought my 2nd iphone (4) from etisalat ( First time Etisalat sells iPhone in UAE), it had facetime, but then after 2 days, the phone started having some softwares, issues i called, Etisalat, they told me to connect it to iTunes and update, after that the phone worked fine , but facetime disappeared. I am suspecting that each region has a custome tuned ios firmware in the iTunes, this is the only logical way that they can control this restriction.
So now, i am trying to find a US iOS firmware and upload it on my 5s, if this works , ill update you then my theory would be correct.
The other thing is its good that they allowed iMessage, otherwise i would have jailbreak the phone.
My last point is , i think that they do not have the infrastructure to accumulate the bandwidth if they allowed facetime, i am sure they have studied the decline in sms, when bbm,imessage,whatsapp tookover, but still they are gaining from the cellular data services part without upgrading their existing systems.
If they allowed facetime, all the 3G ,4G satellites will be flooded with facetime users, as message bandwidth is quite less, when compared to voice and video.
I am also frustrated that since, viber and skype, work, why dont they allow facetime !