Add-Ons are features that are added to your account for a price. Most services is an add-on at a set price for the month. By optioning for Add-Ons, you pick the service features that you would want. Don’t worry, you would still get all of the standard features that you would expect from a phone line. As defined, this service will be a Personal Communications System so it wouldn’t make sense to not provide the features you would need. However, you can get features you would want.