As I understand it, there are some countries that allow, multiple ADSL ISP's on one line.
Here I'm told that a Service provider lock is a function implimented by the regulator and see no reason to lift this situation.
I am also led to believe that should the lock not be in force then you could in practice just change log in name and the RADIUS server at BT (assuming you are on BT) will just route you to the different ISP.
OFCOM - a regulator thats pointless, if they had any teeth, they'd make all LLU and Cable operators have a USO as well, instead of just cherry picking.
Shunts...