I was comparing the cost of the new Sky Broadband + Calls + Line Rental of £14/month (assuming you are a current Sky customer) with my existing deal with BT at £42 - for an inferior service (BB same but calls only after 6pm).
The £28 I save each month goes a long way towards paying for my Sky 'content' package. The question I ask of BT is 'how can you justify your pricing'?
So you do need BT (and their Line Rental Tax) but the Sky call package is only £5/month.
Also reports suggest the role out over the UK will take time and not everyone will be able to join immediately - it all depends upon your location. However you can register now no matter where you are.
I've just requested this myself but only the base broadband package, free broadband and free wireless router for just £40 connection (although I think it's unfair to charge this as my bt line is already enabled so will beg this for free also when they call me!).