Will my iphone 4 with version 5.0.1 (9A405) work in india

I have a Iphone 4-16gig with ATNT service provided it is not jail broken & unlocked it is on version 5.0.1, Iam visiting india in couple of months,i just want to know if I purchase GEVEY ULTRA well it work and if i cone back to us will it work with the ATNT .I will be thankfull if you could help me in solving the problem