As a tangent, I've found that phone + email are the truly general options across what is anecdotally to me the Balkan social networks. I've also come to realize that everyone views their social network as obvious, and everyone also loathes to download anyone else's social network app.

But email + phone is international, nobody feels like you burdened them by asking them to get a Google account, and nowadays email and phone is all managed through a synced solution on your phone / devices. As a "workflow", contacting someone via phone or email can feel as fluid as any other app.