A google search brought up something called jnet mobile for blackberry filtering though the site doesn’t currently seem to be working for me. (The posts I found were from 2008 so it could be it no longer exists) According to some old blackberry forums I found, it sounds like it is for people with BIS who connect to jnet’s BES network which filters content. Anybody who uses their own company’s BES would have to have the company set up filtering for them.
There are apps that will block the browser all together as well. (Appblock)
There was a big pdf going around that was given out at the Flatbush asifa that probably discusses this issue. I haven’t read through the PDF yet. If not, call TAG and they might advise you.