The Customer Voice license model
The Customer Voice license model is based on the number of survey responses received. You can send as many survey invitations as you need; what is measured is the actual responses to the survey. When you purchase a Customer Voice license, you start with the base license of 2,000 responses per month and you can purchase add-on licenses in the increment of 1,000 responses per month. For example, if you plan to receive 5,500 survey responses every month, then you need to buy the base license of 2,000 responses and four add-ons to get 6,000 responses per month (since the add-on is available in increments of 1,000, you need to round it up to the next 1,000).
If you have a Dynamics 365 for Enterprise license, which includes Dynamics 365 Sales Enterprise, Customer Service Enterprise, Field Service, Marketing, Human Resources, and Project Service Automation (see the complete and up-to-date list at https://aka.ms/CustomerVoice), then your first 2,000 responses...