"Mikee, the free wifi in McDonalds is fine. You connect through a wireless modem. If you are trying to connect through a T-Mobile dongle, you won't be connecting to The Cloud but to T-Mobile and will need to get a T-Mobile signal. I don't use a dongle at all. I just log on usng the wireless modem in my laptop and follow the instructions.
In McDog or Wetherspoon you will be asked to register with The Cloud but it doesn't cost you anything. Once you have registered you can connect whenever you want without bothering with the dongle.