From what I understand, SPRINT iPhones in the U.S.A may not actualy work with METROPCS due to differences in frequency
(metroPCS shifted to GSM, while Sprint remains on CDMA technology)
Even if you got it unlocked you would have to check with METROPCS. Normally Sprint iPhones are meant to be used outside of the U.S.A or with sprint themselves if you are planning to unlock it,.