Once you have narrowed down the field of potential VOIP providers, you need to check to see if all of them offer e911 service.  This is very important.  Many providers out there do not offer 911 service for their VOIP service which can have catastrophic effects.  There was a news story a couple of months ago about someone down in Houston who had been shot, as a family member frantically dialed 911 on the VOIP service they found out that their VOIP provider did not offer e911.  Not good.  Mr. Thrifty recommends that if a VOIP provider does not offer e911 that you move onto someone else.  It is not worth running the risk.