As they say your best camera is the one you have with you. The portability of a smart phone allows you to capture any spontaneous event that would typically require someone carrying a full camera at all times.
I like the concept of the Olympus A01 lens that connects via Bluetooth to your phone effectively eliminating the weakest part of a phone camera and reducing the footprint of the traditional dslr. I will probably purchase the second gen one since the first one still has some minor bugs, but works as an upgrade to your phone camera.
You can carry the lens in your car or whatever to ensure it's always with you, and since it's Bluetooth doesn't necessarily need to be attached to the smart phone to take photos to give you better shot placement if need be.
http://www.getolympus.com/us/en/air-a01.html