One of the best uses of a smartphone is to supercharge your workouts and motivate yourself by using an App to track and compare your outdoor activities. Save each run/ride and compare to previous speeds to challenge yourself.
My favourite app is called Cyclemeter GPS which obviously by name is made for Cycling but can also be used for walking, running or any other outdoor activity. There are many other great workout apps out available on the App Store or on Google Play.
The GPS in your phone tracks your location and calculates your average speed. May of these Apps also work with other accessories including heart rate monitors, bike computers and of course the new trend of smart-watches. They can also upload the activity to third party websites like DailyMile and Strava. If you want to share your workouts you can do this as well and the apps will auto-post to Facebook and Twitter.
Cyclemeter creates webpages that you can share or view to see the stats on your computer, here are a few of mine: