I would assume not allowed just like cell phones arnt allowed to be on. Plus you need to be in range of a tower. So depending on where your flying could casue an issue as well.
In general, it just won't work. In some instances, with varying altitudes, your card would be able to get service, but it uses the same EVDO abilities like a phone, so it would be "disallowed" via FCC regulations. Some airline companies provide WiFi on flights, I beleive Delta has recently joined in.
But short answer, no, it won't work. At least it shouldn't. And it frowned upon by the airlines.