VOIP is very dependent on upload speeds of your network. The more stable your connection the better VOIP/SIP reception you get. If you're on a WiFi, QOS makes a lot of sense. If you're on a 3.5G network, it all depeds on your Telecom company and your current location. Just a few hours ago, I received a call on my GV account on HSDPA+ network, and I got very clear reception. Unfortunately, the SIP settings on the N9 (or even the Nokia E Series for that matter) has limited settings that we can tweak, unlike a stand alone gateway (i.e. SPA3102, PAP2T)... Bottom line as with any SIP/VOIP setup, everything is dependent on ones connection speed's priority.