I've tested VOIP over Boingo by discretely running a couple of echo tests using various services. I really don't recommend it.

While Boingo blocks most services (you connect to the services but they mess with the SIP packets) within ten seconds of the connection, you can VPN around it (don't use PPTP). It really turns on the bandwidth consumption of the other passengers.

Then you have a ton of background noise and basically have to talk into the palm of your hand to avoid drawing attention. People on the other side of the call will tell you to speak up and you really can't. Remember you are violating a dozen different regulations making the call. You basically need a window seat, the earbud mike in the palm of your hand and talk into the window. Alternatively, you need to have a friend in the next seat who will tolerate your activity and pretend you are conversing with them.

At the end of the day, it rarely works and it is not worth the hassles you will get. I stick to text messaging. While you could sneak off a two minute call, you can also get the message across via text messaging and via email.

For Americans, I recommend a free Google Voice account for a text messaging number; for Canadians, TextPlus gives you a free Canadian number which you can text with to any Canadian mobile phone (and US ones).