I remembered reading this story earlier this year about Dtv having their installers lie about the need for a phone line:
In spite of all of that, I have been a Dtv customer for 6+ years and I am considered an "A-List" customer. I have two SD Tivo's, one HD Tivo and one of their new non-Tivo DVRs and I am not going anywhere. I had to go to Time Warner Tuesday because my Mother's DVR quit working. I stood in line for 15-20 minutes only to be told that even though I knew her name, address, phone number, SS# and blood type, they wouldnt exchange the DVR because I didnt have her ID with me. I asked her if she was joking and she assured me that she wasnt. I told her this just reminded me of why I left TWC years ago.
That having been said, I have phone lines hooked up to all but one of the Tivo's and they all work just fine with or without a phone line.
dbstalk.com and avsforum.com are two good sites to check out for additional info.