Starting this month, Delta will be introducing free in-flight messaging for all of its customers.
Specifically, Delta seems to be offering support for messaging through iMessage, Whatsapp and Facebook Messenger.
There is no word whether other messaging apps are supported, but if T-Mobile's free in-flight texting is any indication, there may be unofficial support for Google Voice and other less popular messaging apps.
At any rate, it's a great feature to utilize if the flight is delayed, and for the people picking you up at the airport.
Alaska also announced something similar earlier this year, so we'll see if this is a trend that all the airlines will eventually jump on.
There is no indication whether normal text messaging—the kind through your cellular network—is supported, but since it seems like customers have to go through the Gogo portal in order to access, my guess would be a resounding no.
Tell us how it fares!