Have you worked out how you compare pricingwise to the RingCentrals of the world?
Then you look at something like OpenVBX, which would be significantly cheaper ($1/month for number, 1c per minute incoming) if you don't mind setting it up.
I actually do not mind the pricing that much, but they have to deliver on convenience 100%, and exposing a private phone numbers is an inconvenience.
Also, the additional external line pricing is not posted on the site - support said it will be about $8 in most cases.
We've been very happy with them, at $20/month unlimited calling.
Just as I personally don't see the point for a land line now that I've got a cell phone, I likewise don't see why I would want to worry about getting a real phone system when we have TellFi.
I have found that many have clunky interfaces that were not easy to set up and configure AND once configured it was hard to go back and change something.
It certainly is nice to have a service that allows ringing multiple phones, and has better support for multiple lines unlike Google Voice, but for now I will stick with Google Voice for my business for the one or two calls I get, as it is simple to use and free.
RingCentral was nice in that it provided an iPhone application and made it extremely simple to dial-out using your 1-800 number from that application, but the iPhone app did not provide access to contacts that were already on the phone [2] and required setting them up through their system with no easy way to sync them (all of my business contacts are stored on my business'es Google Mail account, I don't want to duplicate that).
[1]: http://www.osnn.net/submitted-news/99624-ringcentral-virtual... (A site I am an administrator on) [2]: I reviewed their services in March of 2010.
Congrats on the launch Jason + Conor!
$6.99/mo, 120 minutes, control outgoing caller id. Cool!