All of in-taxi operations could be done by a phone or tablet app. A driver can receive job dispatch info online, get GPS directions to the pick-up and drop-off, that GPS data can be used to calculate the fare, and the payment can be received by PayPal, or another online credit card payment. I'd be surprised if someone hadn't done this already, or wasn't working on it. So will it be long before we see it happen, or will we still have individually-sold hardware to do each little job?
Mokalus of Borg
PS - You could probably do it now without any specialised app.
PPS - Because texting, GPS and PayPal already exist.