I have an Orange PAYG mobile, but I can't access Stack Overflow from it because the provider (Orange) has flagged the site as 'adult' content.
For me personally, this isn't too big an issue as I have a contract mobile too that does allow access—but I'm assuming it may be an issue for many (and not necessarily limited to the one Internet provider).
I requested a review of the site a few weeks ago, Orange replied today with:
Your request has been actioned and the content is confirmed as only suitable for customers over the age of 18.
No apparent appeals process... thanks a bunch, Orange!
I'm not sure if Stack Overflow is too bothered by this, but I thought it best to let you guys know. It seems unfair for anyone to prevent access to SO for that reason, as this is surely one of the least 'adult' or offensive sites on the Internet.