Chiltern Railways have started a trial of e-ticketing sent to passengers' mobiles. I hope to be able to try this service over the next few weeks as Chiltern Railways provide the trains that run almost to time when I have to go into London rather than LUs' Met Line.
The only issue seems to be that you pirchase the tick online, but I guess phase two might allow M-Payment. Then again looking how expensive a train ticket is my ARPU figures would go through the roof if Orange were to allow me to pay via my contract.
Watch this space I'll post an update when I have tested the system.