What are some alternatives?
MightyCall - Virtual phone system that lets you run your business from anywhere.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Grasshopper - Grasshopper enables entrepreneurs to build a virtual office that connects callers to employees, wherever they are.
JustCall - JustCall is a program that allows companies to use a cloud based call service with several important features that make the program perfectly suited for sales teams as well as support teams. Read more about JustCall.
Dialpad - Switch is a cloud-based phone system built for Google Apps users.