I called Tru Cab when I got stuck outside Durant's waiting for my scheduled cab, that was already 25 minutes late.
I was told that, since the drivers are independent contractors, the cab company couldn't guarantee an ETA on a pick-up time. The very nice gentleman I spoke with said, "All I can do is send out the request & someone will call you if they're in the area & available." Which they did, after I was halfway home-- I was lucky enough to flag down another taxi.