True, but here things went a little differently. Carriers here charged per SMS sent, and had plans with things like "includes 100 messages per month for free!!!

True, but here things went a little differently. Carriers here charged per SMS sent, and had plans with things like "includes 100 messages per month for free!!!" and extra SMS packages sold at a discount compared to the standard price, even years after they had began providing Internet (2G at the time). People sought cheaper alternatives, and for a while several messaging apps were used, but WhatsApp was so convenient compared to everyone else (using the phone number as username, no password required, was a genius move), that it was already becoming the standard before Facebook came and acquired it. Carriers noticed their error eventually, and stopped charging for SMS, but by then it was too late. They even tried using the tribunals to block WhatsApp, without success, and technical measures to degrade WhatsApp's protocol and block audio and video calls on it, which also failed legally. So they eventually relented, and now offer packages like "n GB/month plus free WhatsApp!!!" (and in small letters: "audio and video calls not included").