The RCA RC930 and a Phonex (forget model) work well. Look for 56k and caller ID capability because some of the older ones only work with 14.4 and TiVo does not get along too well with those.
I am using a wireless phone jack purchased at RadioShack, their own version, not RCA (although it may be made by RCA). I haven't had any problems with it, and have been using it for about 2 months now.
I was surprised to see a 50-foot phone cable inside the TiVo box, and their statement that you really don't need the unit attached to a phone continuously (thus the reason for the 50-foot cord, just connect it to an existing phone jack up to 50-feet away when you want to download the latest data and/or software). However, I didn't want to miss out on any program information, so I went with the wireless phone jack. It probably didn't cost much less than having the phone company come out and put in a permanent jack, but it was much less of a hassle
Peggy