For the past few months Sky have been sending me these half price offers. You need a working dish and digibox, otherwise additional charges apply. T&Cs state that the offer is only available to former Sky TV customers who have received the mailer, but I know that in the past people have successfully taken up similar offers with Sky without having received the mailer.
Call 08442 411 356 - quoting SkyTV6
12 Months half price any package: Customers can enjoy any Sky TV package for half price for 12 months: Sky TV from £9.75 a month, Sky TV with Sky Sports 1 or 2 from £15.88 a month, Sports Pack includes Sky Sports 1 and 2 from £19.87 a month, Sky TV with Sky Movies 1 or 2 from £13.75 a month, Movies Pack includes Sky Movies Pack 1 and 2 from £17.75 a month. You will pay the full price for your new package thereafter (Packages from £19.50 - £52 per month). Please note you need to give us 31 days notice to change your package. If you change your option during the offer period, you'll pay the full current monthly price for your new option. This offer does not include stand-alone Premium Channels, Sky Box Office, pay-per-view services or the HD Pack. Offer conditional on you having a working Sky minidish and Sky box or charges and set up wait times may apply. One voucher per household. General: Offer end date 24 December 2010. Offer only available to recipients of this mailer who are former Sky TV residential customers in the UK, Channel Islands and Isle of Man. Conditions of your previous Sky TV subscription contract will apply. Offer cannot be taken in conjunction with any other Sky offers except those offers stated within this mailer. You must get any consents required (e.g. landlord's). You must be 18 years or over. Channels/programmes & prices subject to change. Prices apply for direct debit customers. For continuous debit/credit card mandate, 50p monthly charge applies. Information only applies to residential customers in UK, Channel Islands and Isle of Man. Further terms apply. Calls cost 5p per minute (plus up to 10.9p connection fee) for BT customers. Calls from other providers may vary. Correct at 4 November 2010.