Facebook expands the free basic mobile internet service, saying it will help billions of people without internet, mostly from Latin America, Asia, and Africa. It now allows any mobile operator to develop under the platform. The service has brought over 9 million people online over the past year with more than half of the users end up paying to access the wider web within 30 days. Source:
This is really a customer acquisition tool for mobile operators where the benefit to them of offering a very light amount of free data is to bring on more paying subscribers to their networks.