The guided setup required a phone and did not work properly with Vonage. It took 3 days to get through the hassle of setting up the TiVo. why not include an RJ-45 jack on the back...then you don't need a list of "recommended adapters" for hardwired networks. that's at least a better alternative to using the phone line without having to purchase something extra.
while i agree that it would be nice to not have the phone line be required, i just wanted to let you know that i did my initial set up with vonage and had no problems so i don't know that vonage was necessarily your issue.
Software revision 7.2 shipped a couple of months ago and it supports network guided setup out of the box. While you still need an adapter - wired or WiFi - the phone line is no longer required. There are still many units in the retail channel with pre-7.2, but new units are being manufactured with it.
The next generation of TiVo HW may have a wired Ethernet port, the prototype HD unit at CES2005 had one and the new HW for Taiwan does too.
And Luke, you got lucky. Vonage normally doesn't work with modems, it is common for TiVo to be unable to do Guided Setup over Vonage, or other VOIP systems.