demonetization and TAM for digital wallets

Today in my conversation with my dad – he mentioned that I was a great supporter of demonetization. However, problems of using digital wallets do exist. Only 30% of people own something like a smartphone in India. What about the rest of the people i.e. 70% of mobile users, almost 700 million people. They use the mobile phone for making calls, thats it. 

How do we make digital wallets accessible, usable and easy for usage for not only the smart phone users, but, also for the non smart phone users. 

I pointed him to TAM – our own IS work. Is there some technology that is perceived to be easy to use, and, also perceived to be useful i.e. solves a problem while being easy to use, specifically for digital wallets.

Is there something – that can make C2C, C2B, B2C and B2B entirely via the digital mode, without the transaction cost overheads that regular banking systems accrue?