a pbp is a pay by phone and a sms is a credit card type payment you can buy a pin by having you or the mm (assuming there is one) go to the runescape main page. the you click start a new subscription. After you get done there you will see pbp or sms or other payment. you click on the one the seller is selling. once you click on one you have to log in to the account you want it on. then you must give them the sellers pin and maybe (depending on what type of pin it is) a phone number.