How The Cloud wi-fi coverage with O2 works!

I was in starbucks today where I live and somewhat ironically there is a T-mobile and O2 shop right next to it.

Anyway I am able to get both T-mobile and The Cloud wi-fi in Starbucks.

When I connected to the cloud with my US iPhone it took me to a special screen asking for my O2 phone number - it said only once would I have to enter it.

I thought maybe it would accept any iPhone MAC address so I put my number in. Unfortunately it told me that my number did not have hotspot access on the account!

This leads me to wonder if I knew someone with an iPhone on O2 if I would be able to access the hotspot simply by entering my friends number? Would my MAC then be registered for his/her account so that only I could access it? Who knows but maybe you can be sneaky and get away with it?!