Instead of signing up for a monthly plan on a notebook data card, AT&T now lets you pay for chunks of data beforehand. Unfortunately, it's really expensive.
You can get a day pass of 75MB for $15, a week pass of 250MB for $30, and a month pass of 500MB for $50. The prices aren't absurd if you only use the thing occasionally, but those data caps are something awful. For example, just loading a website will get you to burn a couple megabytes, and a heavy email session with attachments will kill half the day's quota. Better to save this for emergencies at the rates AT&T is offering. [AT&T