Smart power is a combination of soft and hard power. Hard power represents well established and inherently effective foreign policies (alliances, war, preemptive strikes, etc.). While soft power stands for all that is time wasting and boring (diplomacy, cultural influence and something about not unnecessarily wasting carrots and sticks...)
Smart power should be phased out due to the development of the smart bomb. Still combining the best of both worlds without the need to get all soft and compromise-y.