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!
Why need to take bitcoin mining into that kind of method? Too much watching of science fiction movies?
Smartphones are not meant into crypto mining. It's for general used.
If your thoughts will be turned into reality then goodluck with the price. People will not just purchased an expensive smartphone just because of the purpose of crypto mining. For smartphone to be turned into powerful miner it needs to matched the specs of some of the good and decent rigs today and there are lots of things needed to be considered. If the price will be just the same with the decent rigs and a person really wants to pursue mining activity then go with the rigs rather than using a smartphone.