I actually went a whole different route the last time I was in the US. I bought a Virgin MiFi at Walmart for $129, and then signed up for their unlimited plan ($50), which gives you theoretically unlimited cellular data access over the Sprint 3G network for a month. I say theoretically because they reserve the right to start throttling you over 2.5GB. There were 4 of us using the Hotspot a lot (it allows 5 devices to be connected simultaneously), and we hit something like 8GB of use (thanks to a lot of FaceTiming home), and I don’t think we were throttled. We weren’t doing anything funky like downloading torrents or streaming copyrighted video, so perhaps that’s the key.
Next time I won’t need to spend the $129, so it’ll simply be a $50 investment, which is well worth it for as much Internet as you need on your various devices. The MiFi has a battery and is TINY so you can easily pack it along for car rides or other mobile use. Walmart also has an exclusive $20 for 1GB offer, but at the speed we blew past that, I think it’s more worthwhile to go straight to unlimited if you’re at all a heavy user.