How to know when your going over your data on iPhone?

I have the iPhone 4 and I know when you call data you get a text saying how much data you've used. A coue days ago it said this:
DATA Usage Est as of 03/28 2:28PM: INDIVIDUAL: 0.559 GB. Usage resets on 04/19.
Today it said this:
DATA Usage Est as of 03/31 01:53AM: INDIVIDUAL: 0.710 GB. Usage resets on 04/19.
I didn't get the message that I used half already but I think I did. When it gets to 1.0 am I done with my data? How do I know when it's over or almost over?

Depending on what service you have there may be an app to download that you can log in and see how much you've used.

There are many data monitoring apps available in the App Store. Check them out

I use a free at&t app which tells me exact numbers, your carrier probably has a similiar one. Search the appstore.

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