It won't happen.
Smartphone for bitcoin mining? you are just destroying your phone.
Smartphone as digital wallet, you can simply download an app / wallet and that's how you make it as your wallet.
You never know! With the help of nano technology we may be able to achieve smaller chips that produces as much power as a full sized mining rigs in future. I mean that is not the reality now but it may become in future. If you were 80's kid, did you ever think that you can carry a computer in your pocket? Because what computer we have seen that time was Pentium one and it required an air conditioned room to run that. Nano technology achieved that impossible and now we carry a smart phone inside our pocket.
So keep your hope high as we don't know where the technological achievements can take us!
If nano-processors are created that will allow to produce more bitcoin and consume less energy, nothing will change, the phones will not be used for production anyway. To say why?
Because such technologies will be used in the production of asic miners.