Well, there are different ways. Depends on what you want.
For example via SMS, there is 40-60% you will not get it, but there are services subscriptions. That is, enter into a contract with an aggregator, create a project. After that, people can subscribe to the service on your site, the frequency you do expose. For example, once a week the subscriber will receive SMS like send SMS to such a number to extend the subscription to such a service on this website, you can unsubscribe this number.
It is possible via payment terminals, QIWI, or even that there percent less.
In General, it depends on what kind of services are going to provide.