Phil Baker relates using Skype on a Pocket PC in Japan, Shanghai: The San Diego tech columnist thought that the mobility of a Wi-Fi-enabled HP Pocket PC running Windows Mobile 2003 with a Skype client would unshackle him from expensive calls or a hard-to-find Japanese rental cell phone. Unfortunately, Wi-Fi abounded in Japan but not much he could use. The Skype solution worked better in his hotel room with a wired Ethernet connection bridged with a travel device. Still, he sees the potential, and it's just in its infancy.
Phil mentions that he'll be flying soon on a plane equipped with Connexion by Boeing. A colleague the other day tried to call me via Skype from a Singapore-departing flight, but I wasn't set up to receive the call. If you're in the air, email me and we'll Skype. (I'm working on an article about this: can you tell?)
Update: Edward Vielmetti has already documented an excellent quality call from a colleague of his who was flying SAS. Unfortunately for the colleague's nearby seatmates, he was talking into his Macintosh laptop's microphone.