Taxis on Twitter?

So I was thinking that Twitter seems like the perfect interface for talking to taxi companies – A quick search didn’t reveal any obvious links for how to twitter a taxi, but think about it – if, let’s say, Yellow Cabs had a twitter account, a DM or a reply with your location & name would be easy for you, and easy for the taxi co to follow and then dispatch a cab. The company, when dispatching the cab, could DM or @ reply to you as well, perhaps with the cab # – tie this into their dispatch interface, and this would happen automatically, saving time and possibly money for the company – customers twittering their requests wouldn’t be tying up phone lines for other people, and the only extra work for the dispatch would be to watch a twitter feed. If people were simply sending co-ordinates from GPS-enabled items, this entire process could be automated, so that cabs within a certain vicinity were simply automatically notified, bypassing a central dispatch all together.