In fact, it might be even cleverer than you'd think. On the move, it's a normal mobile phone, but as you saunter carelessly to within the confines of your home, the Fusion system automatically transfers you to a Voice over IP call, using a BT broadband line and wireless router.
Why? Because it's cheap, says BT, at about 5.5p/hour off-peak to a UK landline. Or 3p/min peak. Cheap, that is, unless you get free calls to landlines as part of your standard mobile phone deal. Or use Skype: not as seamless, but as free as fresh air. Plus, there's your BT line (at least £10.50/month) and your BT broadband subs (at least £17.99/month). And the BT Fusion subscription, from £9.99/month at launch. And, um, anyone who calls you will be charged as if they were calling a mobile.
Still, it offers King Size simplicity, especially for anyone who doesn't get good mobile reception in their house.
If you're itching to be one of the first, sign up here: www.bt.com/btfusion