Good article, as an O2 customer and an employee I was following todays events regarding this with interest, I was pretty shocked about it and it was a bit of a WTF moment when I came across tweets about it in my twitter feed before it clicked to why we'd be putting a mobile number in the header.
As usual we were kept complete in the dark what was going on, but I don't really think it mattered as I only know of one call about it in my team, I think the majority of consumers don't care about these things, they were up in arms when the VAT went up to 20% and they were paying a little extra and if everyone was overcharged a few pennies they'd go nuts about that, but mobile numbers being leaked to websites isn't a big deal as most of them will put their mobile number on facebook, share it with the world then "like" those sites and friend strangers for extra sheep in farmville anyway.
I'd love to know who those trusted partners are too, the only information released to the front line staff pretty much mirrors what's on the blog, there's a few obvious ones such as O2 sites and 3rd party companies such as bango.net (who we use for payments for our age verification system) and a promotions company who were dealing out Amazon vouchers for people taking certain deals. As a mobile number is not seen as PII then I suspect they'll keep us in the dark, but it would be good to know especially if any of the "trusted partners" are social networking sites and although a mobile number is not deemed to be PII it can quite easily be used for billing someone when it comes to premium SMS.
Until I know for sure who's got access to my mobile number I think I'll go back to tunnelling all my mobile traffic through a VPN which will take up extra bandwidth as they wont be able to compress and cache every site I visit and downscale every image I view.
Anon for obvious reasons, usual disclaimers about views being my own blah blah blah...