Turn off cellular data when you're not using it may help, go to settings>general>Networks>Cellular data off, it will stop data usage coming to and from the phone, you will not be able to access the browser or update apps unless you are connected to wifi, good luck!
Congrats on upgrading to the iPhone 4! As you have experienced, the iPhone is a device that consumes a lot of data. That’s one of the main factors that attract people to it, the device ability to efficiently process data. Like most new phones, we all have a certain level of dependency on the device. Below are a few ways to effectively use data while reducing the amount used.
• Use wi-fi when it’s available. (I can stress this enough!)
• Turn off GPS tools and other data apps when you are not using them.
• Adjust email push notifications. (I prefer emails to be pushed in hourly increments)
• Turn off iMessage. (Especially if you have unlimited text messaging)
• Adjust Social Media notifications. (Facebook postings, Tweet mentions, etc.)
• Be mindful or streaming services or use streaming while on wi-fi. (Internet Radio, YouTube, etc.)
• Reduce the usage of Siri as she uses data also. (iPhone 4S only)
If all else fails then maybe a higher data plan is the best option. Although I am unable to recommend a 3rd party app to help monitor data usage on the iPhone, there are several options available in the App Store than can assist you. As always, I suggest calling #DATA to monitor the data usage on each individual phone so the user can be mindful of how much data is available. Hope this helps.
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i'm not sure why it uses more, but it does. google "iphone uses too much data" and you will see a number of threads on other forums with your complaint. some came from previous BB users and some from previous android users. it appears that iphones simply use more data to do everything. the only suggestions i came across are "turn on wifi," turn off cellular data," "turn off location services," etc, etc......which all seem to make a smartphone sort of useless. sorry i have no solution, but google that and you can read up on many threads about it.