I can't use iMessage on my ipod touch 4th gen running on iOS 5.0.1

i can't use my imessage on my ipod touch 4th gen running on iOS 5.0.1 here in UAE...my friend using an iPhone 4S and its totally working...few days ago it was working in the philippines...but now im here at UAE it doesn't...but the question is why my has an iPhone with an imessage working just fine...we are both here in UAE...please give me a positive response..thanks in advance.