i want a new phone but....

it's a kyocera kx21 strobe/switch back from virgin mobile. question is u can buy them unlocked and i wanna know if it can b used on the sprint network. i really don't wanna go to another network just for a phone. believe me i've thought about it, i wanted a razor and a sidekick but don't want to go through the whole change and all. can anyone help or give advice?