I'm using a Huawei E220 HSDPA USB Modem and have been using Cheetah watch with it for 12months. Leopard installed now OSX 10.5.5. No problems at all and would hate to be without it. Worked fine on my PPC iBook and is now installed on my MacBook Pro.
http://m.ac.nz/cheetahwatch/
ps. Blog looks interesting, we are traveling around NZ in a Motor Home "Tukawyle', North Island for two years, now in the South Island