In Trinidad, for example, on Digicel, one of the two largest mobile operators, using Whatsapp does not count toward your data usage. But any other messaging apps do.

Observe the "extras", http://4g.digiceltt.com/en/pricing/4g-data-rates

I wonder if this usage is being subsidized by Facebook. And if this practice occurs in other countries. Because in practice it is a blow to Net Neutrality.