This is not a black and white scenario as you have characterized or how Mark Z has characterized.
As more and more people come out of poverty, they will be able to access basic services such as water, electricity and data plans. There is no reason why data plans is the only service among the three services that needs to be free. If it is free, it is the government that should provide it rather than private corporations whose single interest is profit.
Now, people who are super poor may not be able to pay for electricity let alone will access free internet.
Either way, FB and bunch of other companies want to profit out of the people who are uninformed and these people may end up buying only services and products from those limited free websites that they get from free internet.
It also looks like the telecom services might take advantage of this and partner with some companies provide selective access to some websites and the biggest losers of this kind of partnership could be companies that dont have enough capital to pay each of the telecom providers to be in their "basic package"