i have no reason not to be calm, im not affiliated with the cm team, just a guy who works on unloved devices
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higher end metro/tmobile devices will have a good bit more support via flashing tmobile stuff, but dont expect metropcs support overall. arocker is amazing on the s4, but just about every other rom is just them flashing a tmobile rom. some of teh lower end stuff like the alcatel devices wont have any or low dev support.
also tmobile's plans are more expensive, they recently upped the price of unlimited and that doesnt include fees/taxes.