My business has several incoming phone numbers through BT, Skype and Vonage. We use them to differentiate callers. We have a couple of public ones, one used for sales, another for enquiries etc. We reserve a couple of numbers for important clients. Recently Hibu, which used to be Yell.com, have been making pestering phone calls to one of our numbers. Sadly for them it is a Skype number. With Skype it is very easy to block calls from a specific source, click and block. There's no extra charge from Skype for this facility. It's a pity that PlusNet (BT) seem unable to offer this type of easy to use facility, free of charge for their phone service to PN clients.