No, iOS 18.3 doesn't install Starlink on your iPhone – here's what the latest update does, and why you should download it
Simply, though, iOS 18.3 does not install Starlink on the iPhone. Essentially, it is packaged within iOS 18.3 as a carrier network settings update for T-Mobile that allows for the connection. It is not on by default, though, and you need to be selected to join the beta after requesting a spot.