I have an iPhone 4. Under Settings > General > Usage, there is a button to "Reset Statistics". After reading the manual, I'm not clear on one point: if I reset the statistics, will the entry under "Call Time: Lifetime" also be reset?
After a quick test, everything but "Call Time: Lifetime" and the statistics under "Time since last full charge" was reset.
It only makes sense that the field "Call Time: Lifetime" doesn't get reset since it shows the the total physical time the phone was being used to call. If it was restored and set up as a new phone I believe that the setting will then be reset since it will be technically a new life for the phone. Unless AT&T/Verizon keeps track of that data through your number. Then you would change your number to reset that field. Though I wouldn't be trying that anytime soon.
I would not recommend reseting your statistics on a iPhone 4S for mine knocked out everything on my phone and I ha to go to AT&T to get it reset again to get my phone back. Everything was deleted.
It clears all of your revived and sent data for calls and it will not hurt your apps