WhatsApp let you send pictures. They came up with MMS but by then everyone was already on WhatsApp.
Now that I think about it WhatsApp really took the country by storm- the only thing that I can compare it with was Napster and Kazaa. And just like those it was all done by word of mouth! No commercials or ads. It was all organic.
Not sure that’s true everywhere. In Slovenia we had unlimited texting way before we had smartphones.
By around 2005 all carriers offered a “teenager” plan with unlimited texting and near zero phone minutes. Data was not yet a selling point.