I'm trying to recall the name of the app that does this, but one of the travel-tracking apps uses Apple's push notification system (which the network treats as "messaging") to send e.g. gate changes to subscribing devices through this "messaging only" network.

The APNS payload is a JSON blob that's limited to 4KB, with a few required pieces of information but mostly free-form, so it's definitely in the scope of e.g. a (text-only) blog post split over a few messages.