Neither Net-10 nor Metro PCS is a supported carrier. You'll have to ask them if it will work.
In theory, a legitimately unlocked iPhone will work with any compatible GSM carrier. Not all features may work, and any issues you have, however, will have to be resolved between yourself and the carrier. Thus the difference between a "supported" carrier (a list of supported carriers can be found here: http://support.apple.com/kb/ht1937) and an unsupportec carrier such as Net-10 or Metro PCS.