Does your iphone warn you when you're using data?

I just got an iphone 5 today and I only want to use data when it is absolutely necessary. I will be connected to Wi-Fi almost always but I don't want to get disconnected and charged for data. Will the phone warn me when I'm about to use data?

The only warning will be that the phone will indicate a number of bars and say "3G" or "4G" at the top of the screen.

It'll only warn you when you're almost over your data plan. You should know when you use data-whenever you use anything with the internet and if you're not connected to Wi-Fi.