I remember seeing it talked about on local news when it was being implemented. It was normal to list “e911 support” on the outside of phone boxes when it was a new feature. Just checked my desk drawer and it is listed on the box of one of my HTC phones and one of my Samsung phones.

E911 can also use triangulation which is isn’t “in” your phone anyway. It’s possible with any type of radio transmission due to plain old physics.