Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Phonebooth - Phonebooth is one of the leading voip providers, providing phone systems & phone service for small businesses.
Mitel - Business Communications and Collaboration
VoIP.ms - VoIP.ms is a VoIP origination and termination tool.
VirtualPBX - VirtualPBX provides hosted VoIP PBX phone services that give small and medium growing businesses a professional, fully automated call answering and routing solution
Loop Communications - Loop Communications provides hosted VoIP business phone systems to small businesses and mid-sized companies.