I'd echo recommendation for American Taxi. Their automated dispatch # is 1-800-244-1177. It will be a flat fee ORD to suburb and they will take a credit card w/o hassle.

It will take about 10 minutes from the time you call until the cab you are assigned shows up at the terminal. If you call when you deplane you should have time to make it to the curb before they show up (at that time of day). Also assuming you don't make an extended bathroom, snack, or shopping stop.