Setting the call duration lets you see how many minutes you speak for a call. This can be set by following the steps,
1. Go to Settings -> Calling -> Call -> you will get a screen
2. Scroll down the screen to find the option Show call duration, set this to Yes. Also set the Summary after call to On.
3. You can see this change to take effect when you finish the call, it will show the call summary.
Steps with Screenshots,
But this call summary will flash for just 2 seconds and disappear. To see what was the call summary you can follow these steps,
1. Go to Menu -> Select Log
2. From the next screen, select the Call duration option
3. Now this screen will show the details like,
a. Last call duration
b. Total duration of all Dialled numbers
c. Total duration of all Received calls
d. All calls, shows the total duration of both received and dialled calls
4. If you click Options from this screen, you can see there is a feature Clear timers. If you click this it will clear all the counters to zero. (It is not recommended to try this option, unless until there is a need)