I had a "friend" hookup hundreds of mac minis, added a decent api, setup icloud accounts, and let it rip. If you get good at sqllite you can make an entire chat app. A message goes out, a message comes in, you take an action, respond, etc etc. Apple shut that down (apple actually does have a unique hardware id they will use), but those were fun times - for my friend. But the cost beat twilios all day!
