Spend 5 minutes looking up how to make a chat bot and be amazed how Telegram is really the only option. I was dumbfounded when rolling my own agent.

iMessage is proprietary. WhatsApp charges you. Unofficial APIs exist, sure, but not my cup of tea.

Then you have Discord or Slack, which are pretty heavyweight when all you want is a simple chat interface.

Telegram makes it SO easy. Bots are first class resources on Telegram and they make them so easy to use.

XMPP is working pretty well for me