The company that I work for has been a Vonage customer for almost 2 years now (ALMOST!), and while we never had any complaints with the service, it really isn't designed very well for a growing small business like ours. I would still probably recommend it for personal VOIP or single phone line (their ATA adapter with built in Caller ID is top notch and the website is pretty easy to use), but if you want more business features I would recommend looking at www.RingCentral.com instead. They offer features such as an Auto-Attendant (i.e.... press 1 for Sales or 2 for Support...), an optional PC based call controller for answering/forwarding calls, hold music, extensions on toll free or local lines, custom ring schedules (business hours, after hours, Morning/Afternoon shifts), Company Directory, and a lot more advanced options regarding how, when, and where each phone line and extension rings.
So if you are looking to setup a new phone system for a small business, save yourself some time and money and go with RingCentral from the get go. We started with two Vonage lines, expanded to three, and then finally decided to switched over to RingCentral when we got our fourth line. It then took almost 3 weeks and 3 phone calls to port the numbers over from Vonage to Ring Central (Vonage had to manually remove the numbers from their database...) and it cost us $160 to cancel the Vonage account because we hadn't quite reached the end of our 2 year contract yet.
For more info on how RingCentral works check out this video:
Next up: Getting my RingCentral extension to work with Google Voice :-P