So I've seen three different models posted on the web the rm-937 which is the global version, rm-938 which i guess is the att version and an rm-940 or something like that.
I don't think the RM-937 will work very well on T-Mobile. First, it doesn't have LTE band 4 (otherwise known as LTE over AWS band). Worse, the phone doesn't support AWS on 3G, either. It DOES support 3G over PCS (1.9GHz), but that requires a refarmed area. Basically, unless I am reading the specs wrong, you would be better off with the RM-940 (AT&T variant) on T-Mobile than the RM-937. At least you'd have LTE in the T-Mo LTE markets.