If it was labeled lost/stolen in Sprint's system then it cannot be reactivated. If noone claimed it as lost, or never told the customer service rep to lable it as such, it should be fine. Also a quick wipe of your data when selling or getting rid of a phone is ##786#, it will ask you for the MSL (Master Subsidy Lock Code), but you can get that from a chat rep @ Sprint Chat, or by calling customer care.

I bought a phone from someone and now I am giving it to someone else. With sprint, if the phone was lost, can it still be used if its activated by another person under another number?