RP GSMA (AT&T) now supports MMS on iOS

Telecom
1

https://help.goredpocket.com/hc/en-us/articles/360001038592-Can-I-use-picture-messaging-on-my-iPhone-with-the-GSMA-network-

Official carrier bundle available for iOS 13.3+.

ETA: (Unverified) On Reddit, claims other features may also be available on iOS 13.3+, including hotspot, FaceTime over cellular and Wifi Calling. https://www.reddit.com/r/redpocket/comments/e9nped/new_features_on_gsma_with_ios_133_update/