AT&T Tilt and Wi-Fi?

So I'm considering buying the AT&T Tilt as a refurb online (MUCH cheaper than in stores) and I was wondering how exactly does the Wi-Fi feature work? Do you have to have a media plan, or can you connect to wireless networks for free? I really want the phone because I like the idea of having a mini laptop, but I don't have/want a media plan to go with it. My college has a wireless network and I also have one set up at my house. Would I be able to connect to these networks for free or will I be charged by AT&T? I'm also considering buying a Blackjack II--so any imformation on this phone would be helpful also! Thanks again!!