When I started the c25k journey, I read up on how to calculate calorie burns for walking and running, and put together a small spreadsheet. It's fairly simplistic, but it gives a better estimate than what you'd get from using a phone-application without a heart rate monitor.
It nees the runner to measure the total length (e.g. using Runkeeper or the distance measuring tool in Google maps), the total duration (Runkeeper or a watch) and the number of minutes spent running (self evident from the podcast). It also needs the runner to estimate the incline (probably not so easy to do accurately unless you're using a treadmill or some sort of map-application like Runkeeper or Garmin Connect that tracks elevation) and the walking speed. Based on this the spreadsheet calculates the distance run and the distance walked, the calories expended on each, and the total number of calories.
If anyone wants a copy, I have uploaded it to the facebook group C25Kers