Cellular call time!

You are kidding .. right ?

It means exactly that ... your total phone call time used .. ever since you had this phone (or last restored it)

 

Yeah. What the person who posted above said. It's just a counter of how much time you've used your phone for phone calls. That's it. It carries over from your backup files and the "lifetime" can only be deleted with a restore but not using your backup. Current period is basically when you last reset it (done from the phone) or last restore from backup.