Now, I believe the operators and owners of these numbers receive fees from the caller (or their phone company) when calls to these numbers are made. BT say they'll absorb these costs.
So, what's to stop me signing up for hundreds of these numbers and then getting millions of people to call me? More likely, what's to stop a bad guy setting up hundreds of these numbers and then infecting those milions of computers in the country that still have modems and are connected to the phone line?
I assume BT have this covered. But I'd love to know how.