Yes....and thats hard to admit as someone who is kind of anti-skype...
I really hate how 'closed' sykep is...but thats another thread.

on the way home from Denmark to The States I made several VoIP calls. I tested 1 skype call and made about 10 SIP/IAX2 calls through my Asterisk servier...there was some latency with both but all in all the call quality was comparable.

Speaking of quality, minus the latency it was better than cell service...and I was using a BT headset (ok...so not exactly FAA approved). I was is FC on a Scandavian flight and it was virtually empy, but still I hate to imagine the day when domestic FC is full of people with WiFi VoIP phones talking from takeoff to touch down.