The Nokia Activity Monitor is great. It displays charts and statistics, in real-time, about your movements while walking or running. It counts the number of steps, and determines the distance covered and the energy expenditure. Summaries are stored in a diary so that you can compare your activity level over longer periods of time. It is most accurate when you attach the phone to your belt, or upper arm, and it also works well if carry your phone in a pocket of your clothing. It might underestimate the number of steps if you keep the phone in a bag that you hold in your hand (as opposed to over your shoulder), and the most difficult case is when you hold the phone in your hand. Inevitably, false steps are detected sometimes, for example when you are cycling or driving.
The Activity Monitor currently runs on the Nokia Nseries phones like N95, N95 8GB, and N82. You must have a memory card in your phone for the application to work. Be aware that the Activity Monitor's use of the accelerometer requires a fair amount of battery power. It does not shut down gracefully when the voltage drops, so keep an eye on the battery indicator during the day, and don't forget to stop the Activity Monitor before you go to bed !