The Yay internal chat is a great way for you to communicate within your organisation.
You can access the following controls by editing a user from the users page then going to the Chat tab:

This will give your users access to internal chat, and, if you have a UK mobile number, SMS messaging. Disable for any users that only need voice functionality.
This will stop the user getting message notifications on both the desktop and smartphone app whenever messages are received.
This will allow the user to make group chats within the Yay app for your organisation.
This will allow the user to make administrative changes to existing group chats.
This will allow users to add contacts outside of your organisation into a phonebook. These contacts can later be contacted via SMS within the Yay App.