A frequent traveler gave this review on RideCharge.com:
I’ve been using this website/iPhone app to book and pay for taxi’s in Chicago, and it works great so thought I’d pass it along. It provides the ability to reserve online and pay for the ride through your phone (linked to a credit card), and once the payment is completed, they send you a .pdf receipt with all the details about the trip (no lost taxi receipts). Also available on the Blackberry.
I’m sticking with my trustworthy cabbie, but if you don’t have a regular driver you may want to think about giving this service a try. The iPhone and Blackberry application and the ability to receive receipts in PDF seems like a big win for frequent travelers.