I've had a problem for a while connecting to BT Openzone from my mac. I get an IP address. I can ping the gateway, but I can't get online. Using my android phone the connection always worked first time. I read one forum post that the problem for one mac user was the DNS not being updated when the network was joined (he had google DNS set instead of BT Openzones DNS). I also had google DNS settings present (220.127.116.11) but removing them didn't solve it for me.
Today, Skype interrupted my connection and asked if I'd like to go online with BT Openzone. It allowed me to use my account with BT to connect and once I'd entered the details BT Openzone is working fine.
I don't know my problem is caused by skype, but on the other hand if you're also struggling to connect maybe this will help you one step closer to a resolution. Please comment if it works or if it doesn't work to help the next reader.