You can participate in xat's open beta program for the Android application. The application is still in beta stages, meaning it is under development and there are no guarantees that the software will work on your device.
How do I log in?
Click the more option (3 vertical dots). Type in your username and password, press "Login", and then click the chat bubble. You may need to login a second time to get push notifications to work. Note that there is no login successful message.
What is the lowest version of Android that can run the application?
The minimum is Android 4.1 Jelly Bean (API level 16).
What is the lowest version of iOS that can run the application?
The minimum is iOS 8.
Are there any other charges I should be aware of?
The application is completely free to use. However, the application will have WiFi and cellular data access, so be mindful of the data you use if you are on a limited data plan.