Club Wi-Fi
Keep in mind that your membership only gets one free connection. If you wnat to connect multiple devices you'll need a card from the desk for each one. I've had mixed success getting additional card which has been trending towards the NO end recently. I have a bit better luck with guests getting their own cards but some of the agents at ORD are very protective of the card.
If you try logging in and logging out make sure you go to the actual T-Mobile page and click log-out otherwise it takes sevreal minutes for the system to realize a device has been disconnected and allow for your MP# or card code to be used again.