Can I buy an iPhone and switch it to a different carrier?

So I've been on eBay looking for iPhones, and I've found a few that I've been interested in. But some are from Sprint, AT&T, or Verizon Wireless. I'm with Verizon right now but I'm planning to switch to cricket soon. I don't want to buy an unlocked iPhone, so I was wondering if I could buy a phone from Sprint or AT&T and switch it to cricket?

No, the only way you can do that is buying an unlocked iPhone. The ones on eBay are unlocked, you can use them for cricket (at least the real ones) buying from a store not unlocked would cost you a 2-year contract. Buying unlocked is 400-500 I believe.