I want to know if i can use a phone that someone still owes on it
No you can't use a phone still associated with another account/line and there is money owed to the account. You also can't use a 4G LTE smartphone on the Verizon Wireless prepaid plans. Since you posted in the Galaxy S3 space, would it be safe to assume you purchased a Galaxy S3? That phone model is a 4G LTE smartphone.