edit: actually, from what i'm reading you won't even get 3G on t-mobile with this model number.
It depends on where you live, I think.
I'm using a Galaxy S2 international version on T-mobile. I only get edge speed at my house, but at my work place, I got "High" (which I suppose is 4g, cause the download speed was approximately 1MB/sec when I was downloading app through playstore.)
And funny when I came to my friend house, which is a rural area, I also get "High" speed.
T-mobile is allow to use ATT spectrum now. They've install the cell tower in quite many city. Not the whole US, but quite many city.