I tried Packet8 for a few months, over a cable connection. The service was erratic for me. I decided I couldn't disconnect my landline, so didn't get the savings i was hoping for. Sometimes my voice wouldn't transmit. I'd call and the other party would not hear me. Service was like others, no answer, hard to get through, except by email. I think it will be a few years before it is a complete replacement for POTS. Other thing they said I could get E911 service in my area when I signed up. After I got the service, they said I could not get it.
Other thing was always had to dial a 1 before every call, even though I got a local number. This confused the family members.
Good thing was unlimited long distance for about $21/month.
Also saw on the news that a child could not reach 911 through their VOIP phone, because they didn't have E911 service. It was a big problem.
Also, like mentioned on other posts - during emergencies - like hurricanes and power outages, cell phones are not a good backup for VOIP, because they are down. The POTS usually keeps on working.
So for me, I guess I'll keep the landline and cell. Might consider downgrading land line to minimum service level and use cell phones and VOIP for rest - but not as big of a savings, but get a second line and free long distance. Could be also big value if make a lot of calls to Canada, or overseas to other VOIP phones.