You do not have to use WhatsApp. If the CSP supports Rich Communication Suite – RCS – then this can be used with your Smartphone.
Instead of waiting for the standards to be completed WhatsApp / WeChat / etc.. developed the OTT application so that it can be consumed. 3G / 4G / WiFi was in place and this helped with the adoption of WhatsApp.
You could even use WhatsApp as an IOT application.
For security please refer to the earlier Whitepaper reference.
Good if you can also highlight what you are trying to achieve with your different questions about Erlang, WhatsApp, Security, etc..
VBR/ Wallis Dudhnath