How to find out iPhone data usage?

I get 250MB a month and I don't want to go over. I used to have an app called 3G watchdog on my android which told me exactly what percentage I had used of my data and warned me if I had almost used it all. I know the thing in settings>general>usage whatever, but I think that counts Wi-Fi as well. I can't find any apps that will show me exactly how much of my monthly data I have used!

I would contact customer service

Agreed^