I got close to signing up for BT Infinity (moving from O2) as the deal seemed good and it includes BT OpenZone. However, I read somewhere (not on their site) that you automatically have to make your box available as a WiFi hot-spot for public use (by BT Fon users). It is apparently possible to disable this by going online and resetting everything (& presumably losing setting info) but you then lose your access to BT OpenZone. There is nowhere in the marketing/sign-up materials that mentions all this and I also searched the T&Cs (all the 4point text stuff) and couldn't find anything about it.
I find this a contemptuous approach to dealing with customers and demonstrates a worrying trend amongst large companies (I've just found out that LinkedIn, under the guise of providing more privacy control to the user, has automatically opted-in its 100 million users into the social advertising program without informing them of the change beyond a blog post).
The lack of transparency that BT has demonstrated will not make me want to use them again - and I wonder whether this merits a complaint to trading standards.