There are router products for sharing an aircard connection over WiFi, and these are mostly for EVDO cards as far as I know. Sprint actually used to sell a product for this, but I don't know if they still do. Do a Google for "aircard router" or "3G router" to see products and discussion on the topic. I myself haven't used this kind of setup since we have several computers and the connection speed would be too slow with several computers online at once.
-------------------- Lisa Gade Editor in Chief, MobileTechReview