Unlocking the spring iphone 4s from sprint to t-mobile for international traveling?

I want to tell T-mobile I need an iphone 4s from sprint to get unlocked because I'm "traveling to another country" will they unlock it for me and will it work with t-mobile then? Please Help

Sprint is probably the same as Verizon, since both of them are CDMA (not GSM carriers), but both offer phones (including the iPhone 4s) that support both CDMA and GSM.

Anyway, if that's true, then Sprint *will* unlock your iPhone 4s for international travel - but once that's done, if you put in a different SIM card, it'll only work if you actually are outside the country and using a foreign SIM - the unlock will NOT work for SIM cards meant to work inside in the USA (such as a T-Mobile SIM card you got in the USA).