3.5 g

If by 3.5G you are talking about HSPA+ which is 4G. Because there aren't carriers that have true 4G so they should all be considered equally.

The Nexus S can use HSPA+ up to 7.2 mbps. Just like any other Android phone on Tmobile that's doesn't have a 4G radio.
It technically doesn't but I believe the HSPA+ is sort of backwards compatible in that you'll see speeds closer to the theoretical max but never there (someone correct me if I'm wrong)