I was Skyping over T-Mobile WiFi here in my hotel in Santa Clara, California when all of a sudden the connection to the internet died. I still had a connection to the WiFi access point it is just that there was no Internet connection. As I called tech support to see what the problem was I tried logging in via my iPhone to see if the problem was the laptop or the carrier.
The iPhone did logon which meant the problem was likely my computer - assuming T-Mobile didn't temporarily cut off my connection because the video was taking more bandwidth than they liked. Once connected the tech support person explained I could only be connected to one device at a time.
The problem is - on a computer when you are connected to the net, a small window appears which allows you to click to logoff. This button does not appear on an iPhone.
So if you have a single WiFi connection with T-Mobile WiFi and want to use your mobile to access it - let's say at breakfast for example, when you get back to the hotel room and want to use your laptop to access the net, just point your iPhone to logoff.hotspot.t-mobile.com.
I hope this helps.