I got a lot of friends in Hong Kong. They are very very rare to use SMS now. The most of them are using WeChat, Line, WhatsApp, those of IM to communicate. That is because IM is free and SMS need to be charged. In contrast, most of my friends in Australia is still very popular to use SMS. I think that is because most of the phone plans come with unlimited SMS. Sending SMS is the core feature of a mobile phone; you do not need to install any app. It won't slow your phone too. For them, that is a better option to use SMS.