Yes.
It has always worked fine for me - suddenly for the past couple of weeks I can't get it to work at all.
It is no longer in the App Store, so I am wondering if it is being redeveloped?
According to the website it is off due to technical difficulties and will be back by the weekend.
I have seen posts on sites from the guy who developed it, and he has always appeared very conscientious in ensuring it is working well for people, so I'd be pretty certain you wouldn't have to pay again.
Let you see mobile use and bills of O2
See some screen shots here
http://www.pageonce.com/cell_minute_tracker_iphone.html