Without going into too many details, the Nimrod fleet in the UK used to (still do?) fly with a teletype system connected to one of the onboard radio systems. The user interface is basically a typewriter keyboard with a roll of paper, but when you type a message it writes to the paper and transmits the information. Received messages are typed automatically to the paper. Two or more teletypes on the same frequency would communicate much like instant messaging on your mobile phone. Other large military aircraft use a similar system for passing messages/orders/reports etc.
Ogre