T-Mobile: text messages between two iPhones on T-Mobile come up green, not blue like iMessages.
Two iPhones in this family: one iPhone 13 Pro and one iPhone SE, version before one announced this month
We've always gotten blue iMessages when we text each other. Then we switched to T-Mobile from At&T.
Now, we both get green message when we text each other, whether we are connected to cellular data or internet data. We have data over cellular toggled on.
Both phones show iMessages active in Settings. We both did the fix of toggling that "off", power cycling the phone and then enabling iMessages. That didn't work. We did it another time and that didn't work either.
When we text other iPhone users, the messages are blue iMessages. It's just a problem between the two of us on the same T-Mobile plan. We have the Magenta Max Unlimited plan and a great 5G UC signal.
For what it's worth we also have T-Mobile 5G Internet but this issue persists even with Internet disabled on both phones.