The main problem I have with this is its a simple Yes / No - well at least my mobile operator's is.
I'm happy to have most stuff blocked, but (for example) they blocked match.com - hardly what you would call hardcore porn, so I had the blocked removed, which then opens the flood gates to everything, including all the illegal stuff(?) - if the filter is too draconian it makes itself useless - but the problem is what we classify as "acceptable" is very much down the the individual.
And that's where all forms of censorship break down - at the margins - we can all agree that kiddy porn etc should be blocked, but download some of the free filtering s/w produced by far-right American groups and you'll find all the gay & bisexual sites start disappearing.
I use a filter list maintained by a group of European Universities - its a pretty good balance, but I can still black / white list sites I want or don't want without the all or nothing typical of blocking at the ISP.