Add-Ons are features that you add to your plan. Most of these features will have a monthly cost to that would be required to be paid as part of your bill. For your per use add-ons, you would need to have money in your funds pool. An example of this will be 411 calling. All of these features are designed to give you more options, and use the resources that would be made available to you. This gives you more options, and more flexibility.