I found a Sanyo Katana 6600, now what?

Hi there, I found a Sanyo Katana 6600, it hasn't been used in sixth months. This morning I call to Sprint customer service and they told me that I can activate this phone in postpaid (two years contract) with no problems, but I prefer a prepaid plan.

1. I really don't know what to do, any idea?
2. I don't know how to unlock this phone
3. I don't know what was the previous phone number
4. When I try to make a phone call I hear a message like this "your account couldn't be validated"

If you were I, what would you do with this phone?

Thank for your time.
Mescalito2

These phones are seriously legit.

I suggest you still get in touch with the Sprite guys and ask them whether there could be any other way apart from signing a 2 year contract. You could a better option that suits you. All the best.