
Have to disagree with JimP's comments. With regards to the marketing - BT's strategy will be to get more users taking more services. I expect they'll tie this in with existing services (ie. Broadband Talk) and it'll be cheaper that previous incarnations (if you have phone/bb).
It sounds like the missing link for BT in terms of Triple/Quad Play (ie. TV/BB/Phone/Mobile).
Comments about competition are just naive - it's up to your phone provider if they want independence for routing calls via BB. Why would they want to give you the option to give them less money ? If you are desperate - then try configuring the SIP client found on many mobiles (that's if they haven't disabled many of its functions and your mobile has wifi).
Nae offence - but I think you are a grumpy Fusion user, but don't have much knowledge on the technology involved and what's possible.