Most of my communications with friends used to be on Instagram and discord. Discord was easy to get rid of because I kept having issues with notifications on it and told my friends that and eventually they got the message when I just didn't receive/reply to anything that they sent me.

Instagram was a lot harder to get rid of. It's a lot easier to pressure people in person than online. I deleted Instagram and told my friends that they could get in touch with me on signal. Initially they were contacting me on SMS, but I used social pressure with my converted friends to get the others on it by making a group chat on signal and constantly referencing conversations on there. Fear of missing out is a big motivator to get people to switch.

Another thing that I did was empathize the features of signal over SMS. I talked about things like being able to see when people are typing, read receipts, profile pictures, stickers, etc. Obviously my main motivation is for security, but a lot of people automatically bristle and have the usual "i don't have anything to hide" talking points so it's been easier to use those other approaches. With the results of the recent US election it's been easier to convince people to make the switch, though.