The problem with charging (any amount) is network effects. When the value of a service depends on other users using it, anything that limits user numbers is a no-go.
The reason the business rationale for WhatsApp (and lots of other digital services) is so wired is because the normal dynamics is supply and demand don't apply.
In a "normal" market, the cost of providing a service and revenue tend to be similar... because companies compete on price.
The revenue potential of WhatsApp is completely unrelated to the cost of inventing or running WhatsApp. The revenue potential has nothing to do with the value to customers. Weird inputs, weird outputs.
The reason the business rationale for WhatsApp (and lots of other digital services) is so wired is because the normal dynamics is supply and demand don't apply.
In a "normal" market, the cost of providing a service and revenue tend to be similar... because companies compete on price.
The revenue potential of WhatsApp is completely unrelated to the cost of inventing or running WhatsApp. The revenue potential has nothing to do with the value to customers. Weird inputs, weird outputs.