This may have caused WhatsApp to get big in much of the EU, but by now many European countries also have unlimited text, so it's not the case any longer.
I thought high costs for international SMS and MMS is what caused WhatsApp to explode. I remember it being the first app with great UX for sending and receiving pics/video/contacts, and then they added group messaging which worked great as well.
No spam because you needed SMS text verification, no ads, no login to remember, just all around amazing app at the right place at the right time.
The only thing I'll add is that, ca 2012 which is when whatsapp started really taking off where I live, intercarrier SMS was slow and unreliable. WhatsApp was fast and reliable.
No spam because you needed SMS text verification, no ads, no login to remember, just all around amazing app at the right place at the right time.