Talk of phones and mobile devices is a bit of a red herring.
Almost all tickets for concerts and sporting events have tickets which contains a barcode. This is scanned on entry. This is an e-ticket. The barcode could also be shown on a phone, tablet etc. The main thing is that however you show the barcode it has to be capable of being scanned.
The same thing will happen with railway tickets. The ticket will effectively be a barcode.
Buy a ticket from a station and the ticket will be printed onto paper (probably bog roll but it might even by orange CCST at some places to kep traditionalists happy!)
Buy a ticket from a station ticket machine and it'll be printed onto paper (bog roll or maybe orange CCST). There might also be the option for it to be emailed to you.
Buy a ticket online and it'll be emailed to you and you could either show the barcode on a phone, print it at a station ticket machine or ask for it to be posted
Buy a ticket over the phone and it'll be emailed to you could either show the barcode on a phone, print it at a station ticket machine or ask for it to be posted
Whichever format the passenger chooses will displays the ticket details in readable form, along with seat reservations as per current practice.
The main issue that needs to be resolved is TfL for cross London journeys and travelcards.
There will be no requirement to own a smartphone to purchase or use a railway ticket.
I really don't get what the fuss is all about.....