Around the World

This is a tri-band 900/1800/1900. I have called Nokia, T-mobile and they all say it should work in the US but when i tried the T-mobile sim cards, it says no network. I cannot figure it out. It worked fine in the philippines. It should not be a locked phone. Has anyone ever heard of this? Is is possible that T-mobile sometimes uses the 850 band in their areas? I thought this band was only for Cingular.