They just put 4G in the Chicago subways a couple weeks ago. That seems like a better solution than public WiFi, which you have to sign in to and is almost always overloaded or poor signal.
Why do you need to sign in into a public WiFi? Why can't it be open to everyone?
1. Our agreement
1.1 This agreement applies from when we accept your request for Service. Please read the terms carefully before activating Service with us.
1.2 By using and/or activating Service with us and/or clicking the accept button on the login/registration page you agree to be bound by this agreement. If you do not agree to the terms of the agreement, do not use the Service.
1.3 We may modify the agreement at any time. In accordance with clause 1.2, use of the Service constitutes acceptance of the agreement current at that point in time.
1.4 These Terms and Conditions do not alter in any way the terms or conditions of any other agreement you may have with MTA for products, services or otherwise. This agreement contains disclaimers and other provisions that limit our liability to you.
... blah blah blah blah blah and on and on.