There are many conference call service providers out there, all of which are competing for your attention.
Some are free, some are not. But all of them compete with one another to keep you, the user, happy.
They all want you to come back, and use them as your main source for free conference calls.
This can most definitely work to your advantage; however, you must be ready to compare the many services available, and determine whether the free ones are truly free services.