I've been a Telegram evangelist since I started using it in 2014. It's been the single most important app / service to me and has allowed me to develop new and build existing friendships through its almost real-time text-based communication. While IM has been available since I had dial-up, Telegram did it better and continues to do so, even with the multitude of added features that have been added on over the years.
I couldn't recommend Telegram highly enough, and I hope it keeps to its core principles and mission for a secure and trustworthy platform to keep us connected.