I have answered a similar question to this on another forum:
There's a good chance the port is blocked by your ISP in Muscat as VOIP there is ridiculously illegal. I think they claim it is some kind of security issue but we all know that's rubbish and it's just some kind of trickery so the phone companies (Omantel) can make more money.
You may also find most legitimate GCC purchased Apple products (such as iPad or iPhone) do not feature FaceTime at all and it cannot be installed without jailbreaking the device.
The only thing you could do is get a VPN and route your connection through there, however this may slow things down as most paid for services are oversubscribed and undersupported. However there are rumours that use of VPNs may become illegal soon (or may have already).
There have been suggestions that a local ISP will provide a VOIP service, although how this will work I have no idea.
I am sorry I could not be more assistance and hope in the future Oman will wisen up and unblock the ports as they have done in some other GCC countries.