Join Date: Apr 2009
Location: Bye Delta
Programs: AA EXP, UA Silver, HH Diamond, IHG Plat, Hyatt Plat, Marriott Titanium, Nat'l EE, Avis PC, Hertz PC
Posts: 16,633
Delta’s in-flight messaging is for internet messaging only (iMessage, Facebook Messenger, WhatsApp), not SMS, and you must be connected to the Wi-Fi to use it.
If you had one bar of cellular signal showing, it sounds like you forgot to put your phone into airplane mode and it momentarily contacted a ground tower.