I'm just back from presenting at the excellent Global Messaging 2009 event in Westminster, on the subject of what makes a good mobile service in the context of mobile ticketing and payments:
Global Messaging 2009 - Mobile Ticketing and Payments
View more presentations from Tom Godber.
It covers some of our standard reference points, like the need for a mobile service to address a user pain point and actually perform better than the alternatives to be used. I think this really applies to selling train tickets from the handset, something that a pure deliver-only model fails to achieve.