I have recently looked into this, and taking on a package deal from likes of C W's Talk Talk or a similar deal from Tiscali. Then I can only see that good savings are to be made. Transferring from BT line rental and calls to a Tiscali package, will result in saving £11.00 per month on line rental (Tiscali and Talk Talk line rentals are free), cheaper phone calls and free weekend calls. Something that BT cannot offer me at present.
I have been a loyal BT (GPO) customer for as many years as I can remember, but the saving on offer are not to be avoided.