Changing phones on Cricket, what if I buy a phone off ebay?

I'm currently a Cricket customer, with an Slvr L7c, and I'm wanting to buy a Keyocera Lingo, cheeply online.. my concern is how do I make the new %26quot;used%26quot; phone work with my number, assuming I purchase a Lingo Cricket phone from someone else?Changing phones on Cricket, what if I buy a phone off ebay?
You can get one used Kyocera Lingo Cricket for about $100, I can get you used one too at that price. The brand new will cost you $200. You can mail me if you're interested.