We had it, but then dumped it only because we both use cell phones as our main line...no one called us on the VoIP phone.
Last time I checked, the FCC was requiring that E911 be available on the VoIP phones for emergencies. This was suppose to be settled back in January of this year. I haven't seen anything since, but stick with the brand names and check before you order it (if they have 911 services).
The only downside with VoIP is that since its dependent on your internet connection, if that goes down (cable outage, power outage, etc) then you can't call anyone. Including 911 services, so keeping a regular telephone line handy (or your neighbors house) might be a good idea.