With the Airport and Airport Extreme Base Stations, they only dial when your computer makes a request for an internet site, or, there is a menu item, I believe it is under the Airport Icon, that allows you to tell the base station to dial (connect just like your notebook's modem). You also disconnect it the same way. I have a little experience with it, as when I have set up Airport networks for clients, I try it out at my Home in Washington (w/o DSL/Cable) and dial up from my computer through the Base Station. It sometimes is a bit bulky, but it's better than my Dad's PC random dialing whenever it is on.
TEG