The nice thing about both whatsapp and telegram are there are no accounts, so they just need to download the app, and they'll show up in your contacts. So all you have to do is convince them to go to the app store and install the program.

From there you just send them messages on Telegram, or start group chats. You likely won't convince them to switch themselves instantly, but if they want to message you, hopefully they're more likely to check telegram, because they'll want to get a better idea of when you were last available.

It's not perfect, but it's something, and hopefully if whatsapp keeps up with their paid subscription nonsense, it will push more people away.