how does chameleon carrier on sprint network lumia 635 work?

[Windows Central Question]

I was given a Lumia 635 without a sim card, the carrier is listed as chameleon and network says sprint, how can I activate this phone? The little info I've found about these phones is very confusing. I saw something about sprint , boost and virgin mobile on these phones, does this mean I can activate this phone on any of these pre-paid carriers by simply inserting one.of their sim cards, or does it have to be sprint if it says sprint network?