The cat is already out of the bag with all of the advancements in encryption software. Even if Apple or Google were to make it possible for the government to unlock an iPhone or Android phone and read their encrypted communications, there are other encryption applications terrorists and criminals could use on most smartphones that Apple and Google could not help the government crack.
These would be independent encryption programs that are not dependent on a smartphone’s operating system. So in effect these represent encryption engines that live inside an application.
I think Open Whisper is one such encryption program. Snowden recommends using it.
Of course, these ‘operating system-independent encryption engines’ are expensive to build, and a clever hacker could likely find an exploit that enables him or her to ‘crack’ it, so this type of software would cost a lot of money to develop, maintain and keep secure. Nothing is perfect.
But it doesn’t make any sense to put so much pressure on Apple or Google when in the end, they don’t control all the keys to the kingdom, even for apps on their smartphones.