This does not match my experience in Germany. If somebody gives you their phone number it is just expected that you can reach them on WhatsApp and i have yet to meet anyone that doesn't use WhatsApp.
That seems true throughout the most of the Western world, excluding the US. I have a big WhatsApp network, but that's by virtue of living in SF and NY. Without big immigrant/expat/world-traveler communities, I think most of the US just uses iMessage or regular text.
