Thanks - am I right in thinking that they're only valid for a limited time? What would happen if I did not request it but then wanted to take out another broadband package at a leter date?

If I wish to leave a broadband provider (Sky in this case) but don't want to sign up with another (as I'm switching to mobile broadband) do I need to request a MAC code? What happens to my account if I don't request a MAC code?

My wife has received 'cold' calls from CapQuest on 2 occasions now asking her if she knows the person living next door but one. Other than this she has no connection with CapQuest and they have no reason to call her. Where could they have got our phone number from, associated with our address and what can we do about this?