Ways of communicating change with the times. Give up your phone for a week and try smoke signalling to your clients or friends. It’s technology that is a part of our daily lives.
If it was Shady’s Private Rail Transportation, then yes, you could constitutionally turn off your WiFi and what not. But the key word is that it is PUBLIC transportation.
Private companies and individuals can take it away anytime, as it is legitimately private and even though you say “public wifi”, you still own it, thus privately owned.