Using GT-I9100 in USA

[Nick]

Hi Michael,

It might be worth going into a T-Mobile shop and telling them your
problem. They probably won't be very technically proficient, but
mobile phone operators do tend to have big databases of known issues
with any phone model they have ever sold (hopefully they've sold
this model at some point), with instructions on fixing it. The
fact that you didn't buy it from them *should* be immaterial, as
it's in their interest to use their network happily.

Nick