Most email is free. Data usage is between you and your ISP or phone service.What is the cost of email in data useage?
My concern is cost, what is the cheapest. Therin is the answer.
Is FB the cheapest, I honestly do not know, but either it is, or it has the market share needed to speak to friends around the world.
The issue is the way we choose to use it.
Personally I have deleted FB 3 times, I dislike the money grabbing purpose. The I come back as I miss my SI friends.
Regards Tony