Hi,
You aren't really passing on any charges, as you're offering a hotspot for a BT service that is paid for in all instances unless you're already a BT Business Broadband customer (which means you should have free minutes per month). There is no such thing as a free lunch anyway, as 'free' services tend to be either very restrictive, slow, or fail due to lack of funding.
As far as letting people access your connection in some way other than Openzone, sure there are. But you should have a think first. You'll need a server to manage and log all the traffic, otherwise you could be held responsible for anything they do on your connection. You'd also need a way to make sure that anyone who connects to your broadband can't get into your router.
Being honest I don't know how good the Business Hub is with regard to being used for an Internet Cafe style thing, but I've no doubt that there are routers out there that are designed specifically for it.
Hope that helps.
Cheers.
Dave A
