[geekdaddy]

If you perform an ESN swap (i.e. your new number is assigned to a new phone), I don't think you'll have a problem. The new user would have to contact sprint and swap your phone number back to the ESN on the phone you sold them. I suppose it could happen but probably wouldn't.

If you're still not comfortable selling the phone unless you can wipe the account info, you can enter the programming mode for the phone. Are you on a stock 6.1 ROM? If yes, Sprint Customer service can likely walk you through it.