the general rule is that if it has a 'prepaid' menu, such as Tracfone, Net10, and Straight Talk, the answer is no. they are locked to that specific company or companies due to proprietary software (airtime balance display and PIN). i think a virgin/Boost will work but only on Sprint...
Unlocking a phone will make it work on (in this case) CDMA carriers other than just Sprint, such as Verizon.