The technical spec says opt out, for which you need to acquire, and retain a cookie on your machine. Lose the cookie - you're opted in again.
I imagine customers will be 'encouraged' to 'opt in' via updated terms and conditions at their ISPs. So, the only other opt out will be by opting out of the ISP altogether, which I will do if my ISP goes with Phorm.
I will also inform my ISP as to why I decided to leave, and I'll post about my decision on relevant websites. I would encourage others to make their feelings about this system clear. However, in my business and professional dealings with the major UK ISPs, I've found their general approach to customers to be (almost without exception) dis-satisfactory in the extreme.
Any smaller ISPs reading - advertise yourselves as 'phormless' and you could get a good little niche going ;)
This isn't true. The researcher named in the article posted above has been given unprecedented access to their system, and they have given him permission to post details of the system. You can detect and block phorm with varying degrees of efficacy as both site owner and internet user.