Going further
Here, to keep things simple, we simulated our chat app on the emulator. However, we could have of course had even more fun if we actually got it running on a set of physical devices. If you are the kind of person with so much money that you can pick up a bunch of iPhones and Android devices on your way back from the grocery store (or just have a lot of friends with the same devices), why not make it a fun project of hosting your chat server on an actual VPS (Virtual Private Server) and connect the project to it? You and your friends can discuss plans for world domination in your very own app!
The VPS that you want to use is up to you, but we can think of several options for you to consider. Check out https://www.digitalocean.com/ and https://www.linode.com/ to fire up your backend. There are also several more specific solutions that enable you to fire up your backend with less configuration such as Heroku. Many of the prominent services make it extremely easy to configure...