I originally planned to make call quality measurements for both Skype and Vonage calls. But unfortunately, I wasn't successful in making those measurements with the tools that I tried. So I had to resort to making subjective judgements of call quality as any other phone user does - by ear.
I was especially focused at looking for problems due to dropped packets. Since VoIP calls are carried within data packets that are digitized for transmission over the Internet rather than over the Public Switched Telephone Network, packet performance is critical. The typical VoIP call uses around 50 packets a second. Any less than 48 completed voice packets out of 50, i.e. a 4% loss, is discernible to the human ear as deteriorated bits of conversation. It would be as if I were talking to you in person, and mumbled a syllable in the middle of an otherwise clear conversation. Higher packet loss can result in longer bits of garbled voice or, if the loss is high enough, entire missing chunks of voice - dropouts.
Using my new Vonage and Skype connections, I donned my headset and placed several calls to friends who are subscribers of each network, i.e. in-network calls. All of those calls were North America-based - four over Vonage, and five over Skype.
Fortunately, subjective assessment of my conversations led me to conclude I experienced no packet-related quality issues at all on any of my in-network VoIP calls. They were clear as PSTN - and cheaper, too. All the calls I made on both services connected - and stayed connected - without a hitch, too.
For my outbound VoIP calls, I made nine SkypeOut calls, and six Vonage-to-PSTN (Public Switched Telephone Network) calls. While my by-ear measurements of conversations judged calls on both networks flawless in tone and clarity, there were some other irritating problems with SkypeOut.
Interestingly enough, the SkypeOut issues did not involve voice, but data - specifically phone keypad tone (DTMF) clarity. I found this problem when I used SkypeOut to dial customer service at my bank and one of my credit card companies. On about 20 percent of my digit presses (such as entering my account number, or a menu choice), the number I clicked on my SkypeOut UI was not recognized. This led me to believe that the data tones transmitted over SkypeOut are less than pristine. I did not, however, have this problem on identical calls I made to the same companies using my Vonage connection.
I made six calls each to my Vonage and SkypeIn lines.Three of those calls were made from my standard land-line phone and three from my Sprint PCS mobile phone. While still in beta, SkypeIn performed well, with no discernable quality degradation. In only one case (cell to Vonage) was there a measurable drop-off in quality, but as I determined by a simple change in antenna angle, the momentary static was due to my cell, not to Vonage.