No phone line required for DirecTV DVRs, although they may strongly suggest otherwise. You can't order pay per views with the remote if there's no landline, but you can order them online at directv.com. Advantage of ordering online is the movie is turned on for all your TVs, not just the one you ordered it on if you ordered with the remote.
Some DirecTV DVRs also have on-demand service that lets you download shows & movies from the internet to the
DVR. IIRC, you can also now use an internet connection, in lieu of the landline, for PPV billing purposes.
NO software updates are done over the phone line.
You can also schedule
DVR recordings for your main TV when not at home by logging into the DirecTV web site from any computer or web-enabled cell phone.