Proudrooster writes "Keynote Systems Inc. made 154,000 VOIP calls during the months of May and June. In total they tested six VOIP providers and seven ISPs. Their
conclusion was that VOIP isn't quite as robust as the public phone network due to dropped calls, lower audio quality, and latency (audio delay), but it is still pretty good. The worst VOIP provider had an availability of 94.8% (which isn't bad) and overall the reviewers were pleasantly surprised with the VOIP test results. Vonage ranked best for "most reliable" with 99.4% uptime,
AT&T CallVantage ranked best for "audio clarity"."
Personally I think 94.8% is pretty awful. I don't think 99.4% is very good either. But there is no doubt that audio quality is getting better. I only maintain my land line now for my HD Tivo to dial out from.