Simply put, efficiency. I don’t want WhatsApp, Zangi, or any other such service. Many of the services seems infested with scam artists that are more interested in what little money I have than the actually be a friend. With that said, it just makes sense to use the default messaging app on my phone. Since I have an iPhone, I support iMessage, RCS, and SMS. If my cellular number is private, then I would not be disclosing my cellular number unless I am confident with you having it.