Free T-Mobile WiFi in US

1. Download the firefox extension for spoofing user-agents: https://addons.mozilla.org/firefox/59/
2. Restart firefox and goto: Tools > User Agent Switcher > Options > Options...
3. Click "User Agents" and then "Add"
4. Fill out the window with following info:

Description: Internet Explorer 7 (Windows Vista)
User Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)
App Name: Microsoft Internet Explorer
App Version: 4.0 (compatible; MSIE 7.0; Windows NT 6.0)
Platform: Win32

Save it, goto Tools > User Agent Switcher > Then click the newly added one.

Browse over to http://hotspot.t-mobile.com/vista/ and you should be redirected to a trial sign-up page.