Newegg.com has Polycom OBi200 (Formerly OBIHAI OBi200) VoIP Telephone Adapter with Google Voice & SIP (2200-4952-001) for $39.99 with promo code EMCTCWU27.  Free Shipping.

• The OBi200 allows you to make and receive phone calls using your high-speed internet, your regular home phone and a “VoIP” Internet phone service provider like Google Voice. This enables you to call free or at a fraction of the cost a traditional telco would charge. Refer to the product page and forum thread for additional details and discussion.