These steps at minimal apply to the iPhone XS, XS Max, and XR since the menus are similar, not sure and don’t remember for older iPhones.
1. Tap Phone. Make sure you are on the keypad.
2. Dial the following number: *3001#12345#keypad
You should be at a screen that looks like this at this point with some menus.Field Test Menu
3. Tap LTE.LTE
4. Tap NAS. It is ok if the information does not display in the exact order as displayed below, its a known glitch. If you get a message saying "Waiting for update" you might have to tap back and go back into NAS a few times, sometimes it takes a little bit of time to load up the data.
Pay attention to "is_ims_voice_supported" and "is_emerg_bearer_supported". These typically share the same value and here's how to interpret it.
Thanks for the write-up, JWeaver! This is extremely helpful!
____________________________________________________________________________ Tacos and Hot Dogs are Sandwiches. We're likely not going to agree on this, but trust I'll work hard to get you an acceptable solution to your issue.