How to delete mobile usuage log iPhone 5?

A friend of mine transferred his data from iPhone 4 to iPhone 5 and along with it came the Lifetime Call Time value which now, instead of zero, indicates more than ten days.
How should he delete this value,
Lifetime Call Time value, which is found under Settings -> General -> Usage -> Mobile Usage

Have you tried:

Settings -> General -> Usage -> Mobile Usage

At the bottom of the screen there's a 'Reset Statistics' button.