There should be an algo written that can only be mined via a smartphone. I could finally dust off all my old worthless phones.
I think it would be very difficult to enforce such a restriction. Smartphones are designed to be able to be replicated on a computer so devs of apps can write and test apps for various smartphones. If such an algo was created then someone could simply run several instances of a smartphone VM on their computer in order to mine the coin that uses the algo