Iphone 5 keeps showing no service on Airtel?

I bought an unlocked Verizon iphone 5 (it is Verizon but its 100% unlocked) in US i put a Att sim in it and it worked like a charm.back in india it keeps showing no service but recognizes the sim. If i do a manual search it recognizes all the networks but won't join one.

Added (1). No it did not, it works with att and tmobile in us

When you connected your phone to itunes, did it say, congratulations your iphone is unlocked? And did you try any other sim?