Your personal assistant in Exile.
The XM8 - also known as "Ex-Mate" - is probably the most important item to have in your inventory as it provides access to critical in-game functions. The XM8 runs its own operating system, called the XM8 OS.
Similar to a personal assistent in form of a mobile tablet, you can use it to connect with other players or friends using the mobile 8G network. When you start the XM8 in Exile for the very first time, the 8G network is disabled. You will then not be able to connect with your friends. To switch the 8G network on, open the settings app and toggle the respective option. Your XM8 will remember that setting, so you do not have to enable it again at a later point. Be aware that while your 8G network is online, other players will be able to see you in the 8G network tab and invite you to parties. If you do not want to expose your online status or receive invites from other players, you can simply disable the 8G network. Keep in mind that you cannot invite other players to your party or territory while the 8G network is disabled. Check the upper right corner of your XM8 display to check the signal strength of your 8G network connection.
To use the XM8, press 6 to bring up the tablet, then press the power button to turn it on.
Keep in mind that if you throw away your XM8, you will obviously not be able to use it.
Also, the XM8 is one of the common spawn load-out items, so every player spawns in with an XM8 equipped. This is also the reason while you cannot sell it for pop tabs.
Since the XM8 is more or less a stand-alone operating system programmed into the Arma engine, it relies on correct Arma 3 display settings. If you run Arma 3 on a resolution that does not match your native display settings, you may have trouble using the XM8. The reason for that is unknown, but Arma 3 requires you to actually know the aspect ratio of your screen and set it up correct in the Arma 3 display options. With the patch 1.56 "EDEN" of Arma 3, Bohemia Interactive has introduced automatic detection of the display ratio of your display. Please ensure that this is correct if you run into problems.