My EVDO modem, the Sierra AirCard 595U, was a piece of junk. It kernel panicked, for Pete's sake! I called Sprint, today, to arrange for its return. I think it's a sham that they say that it's compatible with Mac OS, since it seems very problematic on Intel, which is now, I think, all that Apple sells. Worse, it's the only USB EVDO device they sell.
I called them today and arranged to return it.
Instead, I am trying to get a Franklin CDU-680 from 3gstore. I think it will perform better, technically, but I'm a bit worried about coverage. It was very hard to tell what coverage was like with the 595U, because it kept failing. My hope is that with the new device, I'll have mostly EVDO and some degredation to 1xrtt. I won't mind having to redial once or twice during the trip, but if I have large dark patches, I'll probably give up.
Wish me luck.