Yup, did the same but suggested SMS instead of email.

Never told them to stop using things like WhatsApp (that's generally counter productive anyways), just that I did due to privacy reasons. Most where fine with SMS, it's on everyone's phone and nowadays so cheap most phones plans include it unlimited (it's all about data bundles and speed here). A year later almost everyone is on Signal after all. Easier with group chats and sending pictures, or when someone is abroad. As as soon as they got some convinience from it they installed the app. A few I still SMS. Also fine.

As long as you're not a jerk about it, my experience is that it's not thát big of a deal.