All browsers (even smartphones) support importing certificate files. The exception are Windows PCs on domain lockdown. Non-corporate-supported browsers might transition to being more friendly to this process instead of the unhelpful and scary SSL warnings provided now.

Phone app traffic that isn't through a browser would be in a rougher situation, but it would be solveable by your major phone app store providers offering their own root certificates. Since there is only Google and Android, any app provider wanting to target all smartphone users would have to get a cert from one of them, and it would probably be rolled into any developer fees and sold as part of a larger security program.