Following on from Stu's PDS scam warning.
Unfortunately both of these are true, current and catching a lot of unaware people out especially the elderly and vulnerable.
BBC NEWS | Business | BT warns customers of phone scams
With the Sky one you'll get a phone call telling you that your Sky Service Pack insurance is due for renewal. If questioned they will say you either took out insurance cover to cover your Sky box against repair and replacement charges or were given free temporary cover as part of a promotional offer which has now come to an end.
They will ask for a credit or debit card payment. This is how to spot the scam. As Sky would actually request that you phone them on their customer service telephone number to renew your insurance, and that their initial call to you was just a courtesy call having sent you at least 2 prior warning letters.
Fraudsters are sneaky basstards, and should have their thumbs chopped off.