T-Mobile UK devices, on their web'n'walk service at least, have a service book pushed to them that contains these bookmarks in a "Favourites" bookmark section. Annoying, isn't it? I put my own bookmarks in the 'BlackBerry Bookmarks' section.
If you delete the service book, all is better - until the service book automatically gets reinstated. It can take a few days though
I've no ill effects so far of deleteing the service book called
WAP2 Browser Config [BrowserConfig]
but as I say, it comes back eventually....