Sneaky, increase the line-speed, so that customers can utilise more data transfer in shorted times, making the average 2-hour surfing session use more bandwidth, then charge by the bandwidth used.
It's also a load of rubbish, most people with sense will see through it and use ISP's such as UK:O who are currently offering 8mb lines for £40/mo (in certain area's only at the moment, although more area's/exchange upgrades are planned.)
I'm waiting for BT to trial and roll out ADSL2+ more than anything at the moment, but at the end of the day this is BT we're talking about... they do have the tendency to be inept rather frequently when it comes to technological progress.