I would assume you would set up a subscription based service where the first month is free and every month after that is a certain fee. This would all be setup

I would assume you would set up a subscription based service where the first month is free and every month after that is a certain fee. This would all be setup with the payment gateway of choice, such as Authorize.net. You would set it up in a manner that would allow the customer to have the first month free, and then Authorize.net would charge their credit card every month for whatever fee you set up. Authorize.net would be responsible for making sure the credit card is valid and processing the payment.