The U.S. lagged adoption of SMS compared to Europe (relatively high prices for texting in the early days while relatively low prices for calling in the same era) but now SMS/RCS/iMessage are the dominant mobile messaging method in the U.S. There’s much lower adoption of third-party services like WhatsApp compared to the rest of the world because basically everyone has those services already on their phone, they don’t have to sign up for a service that not everyone might use, and it’s basically free on every phone in the U.S. now.