I must admit I find some of the frequencies of carriers, especially for data really confusing so perhaps somebody can clarify this for me.

I had available a Telecom HTC Sensation. My daughter in the US was using a Nexus S (bought here) on T-Mobile and was getting 3G reception fine. But she has to send it back for repair so I mailed over this Sensation for her to use in the interim

Of course no problem with voice/SMS but she says she is only ever getting Edge.

Now GSMArena isn't the ultimate source of information but they for the Sensation (they don't say which model) it should receive

3G NetworkHSDPA 900 / 2100 HSDPA 900 / 1700 / 2100

Now T-Mobile appears to use

1700 MHz/2100 MHz UMTS AWS

But since this is a Telecom version the radio might only be HSDPA 850 / 1900 / 2100. That would explain why it worked fine on Telecom and 2D here with 3G reception but only gets Edge with TMO since there is no 1700?

Does that sound right?

I guess that explains why her Nexus S works on TMO since it has HSDPA 900 / 1700 / 2100.

Does that sound right?

As an aside she hasn't complained since she usually uses wifi and only mobile data rarely (even though she is on an unlimited data plan with TMO!)