Lifelong US citizen here - I've barely heard anyone mention it in person my whole life. If it wasn't for reading about it in discussions like this, I would probably never even think about it. iMessage, social media DMs, and regular SMS seem to be the most common in my experience. Signal/Telegram are pretty much only used here by tech people and/or people discussing not-so-wholesome things and I'm always surprised to see people on HN talk about moving their whole family to one of these apps or using them more casually in general.