I just got the new VirginMobile wifi device (runs off the Sprint network) and it is AWESOME!!! It's the size of a fat credit card, and I can use it anywhere that Sprint has service.
It is a no-contract, unlimited data 3G device for $10 /10 days (100 MB limit) or $40 a month (unlimited). It loads -- BAM! -- here in the urban area. Don't know about rural. But it's going to be my traveling companion from now on. You do NOT hook it to your computer. It just sits nearby. You can run up to five mobile devices off of it. It's got only WPA security, but that'll have to be good enough.
On Edit: Funny ... it does pretty well with YouTube (at least as well as my home DSL -- a few streaming farts here and there), but the picture-heavy Huffington Post gives the card terminal gas.
I had a few hiccups (staying with the bodily metaphors! ) getting it going (the web site for signup wouldn't connect for me -- had to call India!) ... but now that it's running, I'm really impressed. When you log in, you go to a page that tells you your useage (handy if you're on the $10 for 10 days limited data option).
If you decide to get one, go to this web site because it's $149 there and at Amazon it's about $240.
Here is a CNET story.