Phone lines are not necessary unless you want to order PPV with your remote on that specific receiver. You can order PPV via your online account, for free, and have access to the PPV on all your receivers. I've had Direct TV for 2 years and never had any of my 4 HD DVRs hooked to a phone line. Initial install tech and a later upgrade tech never blinked an eye at the no phone line connection. Actually, neither ever mentioned it.
The only reason I have my DVRs hooked up to the phone line is for the caller ID on screen. If that's not important to you, save your money and concentrate on getting an internet connection which at least bring some new features and access to on demand programming.