It seems right now, assuming you're in the test (is anyone that is not working for Apple?), an emergency button (no voice, no text, no nothing, other than the fact that you pressed the button and a location, not sure how accurate) (I guess maybe it's as featured as the Google feature)

MAYBE in the future text messaging service. Text only.

Note: Text messaging currently actually works on some Samsung phones on T-mobile, if you request to join the beta.

https://www.pcmag.com/news/t-mobile-begins-cellular-starlink...

Emergency SOS over Starlink works on recent pixel phones, which appears to provide text chat with emergency services:

https://support.google.com/pixelphone/answer/15254448?hl=en