Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
VoIP.ms - VoIP.ms is a VoIP origination and termination tool.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Loop Communications - Loop Communications provides hosted VoIP business phone systems to small businesses and mid-sized companies.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs