If I buy an unlocked sprint iPhone can I use virgin mobile?

I want to buy an iPhone for cheap but I don't want to spend all that money on a vm one. If I buy a sprint one can I switch it to vm? I have read articles and some say that you can if it's sprint. I just want to be 100% sure you can before I buy one

Yes ofcourse you just need to get it unlocked.

http://www.iPhoneFactoryUnlockUSA.com

You just need your iphones imei number, and you can unlock your iphone for free at the site.

I personally recommend this site, as they unlocked my sprint iphone 5s for free.