I've been looking for the best solution for posting from the road. The Aircard Page has some good info on using the Sierra Wireless 555 card. The downside is that it disables the normal serial interface for the PCMCIA card so it would mean switching back and forth to download images from the cameras. However the page at the bottom tells how to configure PPP for OS X to use National Access (formerly Express Network).
The next problem is the lack of a Motorola v.120e on the list of modems in 10.3. A few tries without success. Finally used the "Sprint PCS Vision" choice. It works like a charm. Surfing away at what internet connect reports is 230Kbps