Here's my hack for United's free messaging. Works on iOS, and makes the flight more useful than before, but not as good as paid internet.
Messaging and Notifications basically follow the same protocol. Even though I usually have notifications disabled, I go and activate it for anything I care about - News, Weather, Slack, Whatsapp (yes I have that silenced). Every single message pops up as a notification. Could be bank alert, Ring alert, homekit alert, whatever ... it just shows. So you can keep tab on things you care about, and if you are really needed, well you can pay and get on the full Wifi. And anyways you can iMessage to communicate if needed.
Messaging and Notifications basically follow the same protocol. Even though I usually have notifications disabled, I go and activate it for anything I care about - News, Weather, Slack, Whatsapp (yes I have that silenced). Every single message pops up as a notification. Could be bank alert, Ring alert, homekit alert, whatever ... it just shows. So you can keep tab on things you care about, and if you are really needed, well you can pay and get on the full Wifi. And anyways you can iMessage to communicate if needed.