I searched quite a bit and settled on Grasshopper.com. Main determining factors were price and web sip client support, i.e., make phone calls from your browser

I searched quite a bit and settled on Grasshopper.com. Main determining factors were price and web sip client support, i.e., make phone calls from your browser or mobile phone. They also have an auto-attendant, multiple extension support, and voice mail to email capabilities.