I'm currently on Lufthansa LH 414 returning from Burton Group's Catalyst Conference in Munich, Germnay. This has been my first chance to try out the new Connexion by Boeing in-flight Internet service and I have to admit I'm pretty pleased. The cost is $9.95 for the first 30 minutes (with an additional 30 minutes free), or $29.95 for the entire flight. Lufthansa handed out $10.00 discounts at the gate for the full-flight service, so I ended up paying $19.95.
A check at http://www.testyourvoip.com/ reports a MOS score of 1 on the 1-5 range, meaning that I'd have more luck shouting than I would making a Skype call.
http://www.dslreports.com reports similar bad news, 111 kbps download speed, 29 kbps up-load speed, not nearly enough to support a voice call.
Even despite these scores, the system appears fairly responsive, it's much better than dial-up over GPRS via my treo, though not quite the WiFi performance I usually get at public access points.
Even if I could make a call I'm not sure I would do so. Given that most of the folks around me are sleeping I don't think they'd take to kindly to me having a voice conversation right now.