How do you figure what phone bands work on which network?

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http://forum.xda-developers.com – Hwllo everyone, I'm on US tmobile, thinking of getting the Xperia V but not sure if it'll work with US tmo hspa+. I compared the One S with the Xperia V on gsmarena and both have the same numbers listed under 2g network and 3g network. Will the xperia v work on tmo us hspa? More generally how do you go about figuring this out? Are the 850/900 etc numbers all you need to look at? (HowTos)