I use a Telos-One-R (R = rack mountable) that I picked up on eBay and this is a diagram of my setup:
Paul has posted some great resources about the topic over at Podcast Rigs especially this post "Telos One, Talkshoe and Skype." There is also a great podcast with Doug Kaye (MP3) over at Podcast Academy that covers this topic.
Both Paul and Victor Cajiao at the Typical Mac User Podcast helped me setup the configuration of my unit - which is done manually with a small screw driver. I also borrowed Paul's unit diagram of a Telos One for my picture. Thanks Paul!
I am pretty happy with how this is working now, but I would recommend doing some post production processing on the phone track (usually your guest) with something like SoundSoap.