Question About the HSPA+ Lumia 900

I have T-Mobile and I do not feel like switching to AT&T. I know that the AT&T Lumia 900 will come with HSPA+ speeds. The question is, will the AT&T Lumia 900 work on T-Mobile's HSPA+ network or am I better off waiting for the HSPA+ Lumia 900 "world" version?