Kali's pretty much hit the nail on the head, here. I'll add this, though: If you only need it occasionally, it's probably not worth the $. I'd say you're better off looking to pick up a WiFi card and find a few hot spots (places that let you connect to their WiFi).
It's mostly a question of what your city has available, though. A city very close to me has wifi connectivity throughout the whole city. Of course, it would cost you $1 million just to buy a small house there, so it's probably not the best investment.
I have WiFi access at work, and WiFe access at home. That makes it more fun to stay at home than to go to work.
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Sorry, that was a typo that I simply had to run with.