Cliff notes version: T-Mobile simply can't talk at the frequency your iPhone needs to receive internet data. MMS messages require bandwidth that simply isn't there. SMS is handled because it is a single burst data transmission and doesn't need that much bandwidth.
You have me stumped... The phone should work with the exception of 3G data speeds with the right apn settings. your link was about the bands to allow the tmobile users to have 3G data... Nevermind