If you have a credit of $10, the 100 minute talk booster has not been applied yet, (if you dial 611 from your phone, you will hear your current account balance). Dial 611 and from the Main Menu, press 2 to buy a booster. Enter your security pin to proceed. Press 1 to purchase a booster. For a talk booster press 1. Press 2 for the 100 minute talk booster. The system will see that you already have a credit of $10 (if this is the case) and should apply the $10 amount to the $10 talk booster.