Watch how the new Pizza Hut app for iPhone works (and expect one for Blackberry etc very soon). Won't be long until you can order a personalised one for your business - no doubt developers are working on this right now.
Think about it: ordering coffee to go as I approach the store, flashing through a food order, setting up drinks for the interval of a show, avoiding the food queue at a crowded football game...you get the idea. With all the upsell and add-on possibilities that staff usually forget.
Driving it is the pervasiveness of the hardware. How to get familiar? Start using this app and roam around the iTunes Store and in the Apps section, use search words like pizza, coffee and restaurant. It's early days yet, but watch for developments...oh, and get an iPhone!
Update: just found Eatnotwait who build an iPhone app for your restaurant and handle the order processing. It will be interesting to get feedback from their users...