If you're looking to transfer porn DVD's to your iPhone, you'll need to get your hands on DVD Ripping software, and then transfer the movie from your computer to your iPhone using iTunes.

Unless you already have an extensive collection of Adult DVD's, and a high end computer, this all seems to be far too much trouble for me. So that's all I cover on the subject.

I've never actually bothered doing this, so I don't have any DVD ripping software I can recommend.