For getting unlock code there should be a good and genuine site which will provide unlock code. I have used unlockgalaxys.com and it is the best. You may try it and after that you always prefer it.
I'm no genius on unlocking phones, however to my understanding, the E4gT is (Sprint) CDMA and Wimax, while Metro PCS is GSM and HSPA+....they aren't compatible systems.
Just my 2 cents.