Amazon offers Prime members the Obihai OBi100 VoIP Telephone Adapter and Voice Service Bridge for $29.99 with free shipping. (Non-members can spend $35 to qualify for free shipping; otherwise, it adds $5.58.) That's tied with our July mention and the lowest total price we could find by $5. This adapter supports Google Voice, SIP, and OBiTALK VoIP services.