There are more than a thousand companies offering VoIP in the U.S. A majority of these companies provide landline replacement VoIP (aka SIP trunks) and mobile VoIP. Examples would be Vonage and cable companies.

It is important to note that Skype (News - Alert) and RebTel have hundreds of millions of users signed up. I am going to ignore mobile VoIP and residential VoIP to focus on B2B hosted PBX providers. This sector is smaller in sales than the Centrex market that the ILECs still maintain. (Sad really.)

The largest provider of business hosted PBX (News - Alert) is Comcast. With its acquisition of NGT and the retention of the smartest person in this space, Comcast has been growing steadily. I estimate that the company has more than 325,000 seats and about $150 million in sales. It should be available throughout Comcast regions by the end of the quarter and rolled out to the channel by the second quarter. If the company can scale the sales process, it could be amazing.

Next up is 8x8 (News - Alert) with more than $100 million in business sales. 8x8 made a conscious effort about 4 years ago to switch from being a tech company to a marketing company – that is when sales took off.

When ShoreTel bought M5, the hosted PBX company was doing about $48 million. Best guess is that they have peaked over $50 million now. Probably tied with ShoreTel Sky (the new name for M5) is the company formerly known as Smoothstone, now named West IP Communications (News - Alert). 

At ITEXPO Miami this year, I was confronted about this list and reminded that Nextiva and Vocalocity should be on this list. Vocalocity was at $25.5 million in 2011 according to the INC5000. Unless Vocalocity had a killer 2012 with 100 percent growth, it wouldn’t make the top. As for Nextiva, a UnitedWeb company, it is unclear how much hosted PBX revenue they have.

The Cloud Communications Alliance members like Telovations, Telesphere, Broadcore (News - Alert), Globalinx, Alteva and Simple Signal are all in the under $40 million revenue boat – with most under the $20 million marker.

It is difficult to determine the actual revenue of many of these companies, as they are private. Also, the revenue comes from MPLS circuits, origination, toll-free and SIP trunking – not strictly hosted PBX sales. RingCentral is rumored to be over the $50 million mark, which would put the company near the top.