[coulsontom]

Unlimited (20mb) BB on Sky is £7.50 and is £16 on BT.
Sky Phone packages are: Weekends: free, Anytime: £5
BT Phone: Evenings & Weekends: £2, Anytime: £7
Line Rental: Sky: £14.50 BT: £15.45 (or £10.75 if pay upfront)

However, BT Sport costs £12 on Sky and is free on BT. (Next year it will cost £15 on Sky and £3 on BT for HD)

Therefore: Sky BB & Anytime calls = £27
BT BB & Anytime calls = £38.45 (at £15.45 line-rental)

Difference = £11.45

Therefore it is 55p cheaper to switch to BT for phone and BB if you want BT Sport.

Though if you factor in 6 months BB for free on BT, you can save £99.30 over the course of 12 months.

Not sure it'd be worth the hassle for most.