Twice the speed of dial-up, but you still have to pay call charges. Ten times faster than dial-up, and always on. Technical problems, and BT reluctance, means it is not as widespread as you might hope. There is also a waiting list for installation. The cheapest way to get broadband, but only an option for those who live in cabled areas.
Speed depends on how many neighbours are logged on.
Cable firms also do not have a great reputation for customer service. The Holy Grail of broadband, completely eradicating the traditional bottleneck between your computer and the net. Now they've got to make the technology work. If they do, it could deliver video and the internet to your mobile phone. Costs may be high because of last year's government auction.