Verizon's BroadbandAccess (cellular broadband) is a service which utilizes a card that fits a PC card/Cardbus slot, which the iBook and 12" PowerBook don't have (15" & 17" PowerBooks do have one). Currently there's only one (possibly 2) versions of the 6 or 8 PC Cards they offer that'll work with a Mac system (with some customization software wise). The Verizon service is available just about anywhere your cell works digitally in major markets (500K + metro areas like Cincinnati, New York, Chicago, etc.).
What the sales people were talking about is the Airport card, which is a WiFi (802.11b/g) wireless adapter that allows you to connect to the regular WiFi hotspots (common in homes, businesses, campuses, cafes, etc.). The range on WiFi hotspots is pretty limited in comparison, but it's by far the most popular wireless internet access method. The Airport slot is not a standard PC Card slot at all and is located under the keyboard.
I'd wager the chances are they mistook your question on the matter as being related to WiFi. You'd be amazed how many people don't know about this current offering from Verizon (even the geeky ones who you'd expect to know something).