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!
but it still a long way, i have seen that in china there are a bitcoin mine as big as a room just for computers, this will need time to shrink a room sized computer into a hand sized smartphone
The sizes of computers these days is shrinking, and we all know that since there are a lot of portable things made in the past. I can't say that smartphones will ever be a miner since we can just stick to what we are using right now.
ASIC means application-specific integrated circuit, and it is designed for a certain or special application and it's example in our case particularly is mining. Making a phone a miner also means making it an ASIC, I don't know about that. The smartphone industry is leaning to the performance, mostly gaming performance, great cameras and special functions so I don't think that will be necessary.