MAC - great in theory
Except if you're leaving BT. then you get an hour long arument with some jumped up little tosser who's trying to tell you, you don't need one, even though the new ISP has expressly requested it, based on not being an unbundled area, even though it is! and then they don't take it as notice, and continue to charge you for three months after you've been successfully transferred!!
In short, I think they were deliberately trying to make it so difficult to leave, that you might give up part process. Took threat of legal action, using the SKY billing to prove I wasn't a BT cusomer anymore, to get my money back.
(don't really like SKY either, as they know less about tech support on BBand than I do whenever I have to call them, you have to get past three layers of helldesk pillocks before you can talk to a tech FFS!) maybe o2 is the nesxt attempt for something better than a measly 1.8meg download, hoping ADSL2+ will wring another 50% out of the copper?!