I've been using a Sierra Wireless Aircard 555 for several years on Verizon's Express Network (claimed speed up to 150kb/s). But it only worked on Windows laptops. Emailing Sierra Wireless for OS X support was an exercise in futility, and I've been constantly searching the web for a solution.
This morning I finally found one! I discovered an
Aircard page on Alex C. Snoeren's site which documents the process! Following the posted instructions worked prefectly for me...
I'm not affiliated with this site, but thought I'd share the knowledge.