WhatsApp is as effectively free as it can be within the segment of the population that needs or wants it.
This is like arguing that free Wi-Fi isn't "free" because some people only use ethernet. If you don't already own a compatible device, you aren't their customer anyway.
This is like arguing that free Wi-Fi isn't "free" because some people only use ethernet. If you don't already own a compatible device, you aren't their customer anyway.