There is a joint venture company that WBD and BT formed. I believe WBD have option to acquire the BT share in that company at two points in time ( one of which I believe has passed). I believe that if WBD do not exercise their option then BT would from a certain point in time be able to sell to other buyers .
Even if BT were to sell there are I believe agreements for continuation of coverage for a number of years.
