Easy VOIP: Obihai Obitalk
Until recently, choices for VOIP adapters were limited. Most service providers used the Linksys PAP2T, which is an old adapter based on Sipura technology. That has changed with the Obi family of adapters from Obihai, which not only serves as a VOIP adapter but also works with Google Voice.
I have been using an Obihai Obi 100 for the last few months. Set up was dead simple. Plug the Obi into the Internet, the outlet, and a phone. Register an account online at obitalk.com, which is used to set up the Obi software. Type in your Google Voice info (or VOIP info) and you are set.
Voice quality is superb. (But I have a super-high speed Fios connection so your mileage may vary.) I can conference call and forward calls easily. The only wrinkle is that chatting may not work with the Google account linked with the Obi but I haven't run into that problem.
It is definitely worth the forty dollars to try for anyone who wants a landline without paying through the nose.