I think I'm going to have to settle for this or similar for non-phones (tablets, desktops). I kept looking for a simple messenging app (username, password... maybe email account) to avoid having to share my number, etc. The first thing Telegram did (like many others) was pull my contacts and display other users in my contacts (based on their number) that were also using telegram.

There just doesn't seem to be anything out there that's friendly, old-school messenging (except for complicated stuff that would be difficult for other users to get setup).