It's not clear! Sensibly it should be 21CN WBC enabled exchanges, but Orange could interpret it as where they did LLU.
Depends on whether WBC covers 85% of all UK homes. Someone here has stats for it. BTw says it intends to enable exchanges serving 90 per cent of UK homes and businesses during Spring 2013.
Also you need to be an existing Orange mobile customer to get BB + Off-Peak Calls for £5 pm.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC