Logged into Salesforce, under Setup go to Installed Packages
Find the FastCall package and click Manage Licenses
You will find the number of allowed and assigned licenses. You can add users here.
If you need to purchases additional licenses, you do so from the App Exchange
Go to the Add AppExchange Apps option to navigate to the AppExchange. You can also navigate from Setup.
Go to MyAccount
Click Modify Subscription to Add Users
If you are upgrading from a FastCall package with a Site Wide License , you will need to assign the FastCall licenses to your users. You will also need to assign a FastCall license to the Salesforce Sites Guest User.