Please be advised that the warning below seems to be genuine - apparently BT have confirmed that they are aware of the details and are investigating.
The scam relates to home and/or work phones (including mobiles).
The scenario is:- Your phone rings and you receive a recorded message;
"Congratulations. We are calling to advise you that you have won an all expenses paid trip to an exotic destination. Please press 9 now to hear further details."
If you press 9, you'll be connected to a premium line that bills in the region of £20 per minute.
If you press 9 and connect, even if you disconnect immediately, the other end will stay connected for a minimum of 5 minutes - at a cost to you of £100 - the message lasts for 11 minutes.
The final part of the call asks you to key in your postcode and house number (which has other serious considerations) and then, after a wait of a further two minutes, responds with the message;
"Sorry, you are not one of the lucky winners." and disconnects, adding a further £260 to your bill!
Unfortunately the calls are originating from outside the U.K. and as such BT and other providers are relatively powerless to act.
The only safe solution is to hang up before the message prompts you to press 9.