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.
My colleague was holding his Powerbook's mic right up close, and talking in a low voice. The Powerbook has a good mic. We ended up mostly using IM to communicate since you can have multiple IM sessions going at once.