Just an FYI to the world: if you need to get online via cellular in Japan, the FOMA A2502 HIGH-SPEED card from NTT Docomo works great. No crashes, supports 10.5 (and 10.4), and gives reliable 7.2Mbps down and 0.4Mbps up within the FOMA????????? service area. (0.4Mbps up and down in the older service zone.)
They now have a new card, the L-02A from LG, which also claims to support the Mac, but I haven't tried that one. UPDATE: I bought one of these yesterday, and it also works great.