If i get an iphone 3g at BestBuy can i activate it at home and unlock it?

Or do i have to get them to do it? Ok i want to get the iphone 3g and use quickpwn or whatever to unlock and jailbreak it... But i want to know is when i get it at best buy do i just check out like i do with anything else, like my ipod touch or do they do something with it there? I heard that you might have to activate it there and i was wondering how that works, if i have to add 2 years to my at&t plan, pay or whatever??? I hope i can just take it home and unlock it and just put my sim in it like a go-phone. Please help me if you have bought one, thanks.. Also and tips on cases, ect would be great! Thanks so much