I'm sure over there in the US you have several choices to go from, sadly in Mexico there's only one carrier using CDMA- EVDO, my options are kind of limited, but here are my findings:
One thing I found in several sites is that your card has to be "activated" to work with your service provider in a Windows machine prior to being used under Mac. I do not know if this is still the case, since it's been more than a year when I first tried using EVDO in Mac and my cards were already activated so I knew they were working properly. If your card is already activated for service you are good to go.
I managed to make work a Kyocera PCMCIA card with my old TiBook under 10.4, but I had to use a tweaked version of the Verizon app to make it work. It did very well actually. Officially there is no support for TiBook to run WWAN natively.
As I do have an iBook and and a Macbook, I though I was out of the EVDO game since both of them only have USB ports, not a chance to use a PCMCIA or one of the new Express cards, until my carrier started selling a USB modem, Franklin CDU550, and boy it works great. I have both, the ibook 10.4.X and the macbook 10.5.1 being able to run WWAN natively.
Just plug and play, the OS recognizes the card and you are good to go. Now I can navigate no matter where I am, provided that there's CDMA coverage...
In conclusion, USB CMDA-EVDO modems works natively under tiger and OSX 10.5.X with iBooks and MBs.
BTW here are a couple of good links with lots of info:
http://www.evdoinfo.com/index.php
http://www.evdoinfo.com/content/view/2147/63/
Hope this helps
