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To the OP, my wife is a stay at home mom, and only leaves the house a couple times a week as well. She also has the 200mb plan, and stays easily under that limit. I keep a pretty close eye on it and she does about 20mb of data every week, so she's always under the limit. The most she uses the iPhone data plan is when we are at church, and even then it's not very much.

I wish I had some suggestions on how to rectify your problem. About all i could think of was possibly jailbreaking her phone and then finding an app that tracks data throughput realtime, but i don't even know if such a thing exists.
 
I would try removing all email accounts. Even when you turn off push and fetching, for whatever reason, the iphone will download email. It might be when she leaves the house, her email gets downloaded. A few mb per day could easily add up to ~150 mb in a month.
 
200MB data plan -- not enough for a new mom at home?

I am new to this kind of thing, however i am really upset and can't figure out where to take my complaint, certainly not to AT&T because they haven't be any help to now.

But we are finding that our data is jumping and we have no idea why, which of course puts us way over and AT&T gets to charge another $15!

So we did a test. We turned off EVERYTHING that could possibly create data on the phone, cellular roaming, cellular data, push notifications off, location finders on google, safari, etc everything we could think of. AND our data still went up! In 4 days it went up 14MB, now that isn't a huge amount i know. BUT when everything is off and it is still getting charged for some data, how can that be? AT&T isn't interested, why would they, they get to charge you. So who would i go to, so that i can officially verify this and make someone listen that MILLIONS of AT&T customers are being charged for data they aren't using? thanks!
 
There is something going on with you guys, because I am on the 200MB plan and don't get these random outbursts of cell data activity.

I am almost always either at home, or at work during the week so have wifi the great majority of the time. But I always leave cellular data on so I can occasionally check web outside wifi and also receive push email (Google Sync) and use visual voicemail. My data usage ends up real low- I'm on track for 100 MB this month, and was well under 100 MB last month (my first month with my iPhone.)

I would recommend to OP that he just turn cellular data off on his wife's phone, and see what happens. It doesn't seem like she really need cellular data at all, but can always turn it on if she needs to check on something. If she finds that she occasionally can't access the internet at home, then there is some sort of interference or range issue, and she's just not noticing the wifi icon go out. The other thing is to test any wireless stuff at home (like the baby monitor) and see if it affects her wifi signal. But that might not be consistent and hard to tell for sure. So that's why turning off cell data is an easy test. It would also be significant if you were still getting large cell data transfers during this time, because that for sure would rule out your wife's usage.

When I first got my iPhone, I generally left cell data off since I don't use it much anyway, and didn't want unexpected data usage. But since leaving it on all the time, that just hasn't happened (even though I get emails while driving, or out and about on weekends.)
 
I would try removing all email accounts. Even when you turn off push and fetching, for whatever reason, the iphone will download email. It might be when she leaves the house, her email gets downloaded. A few mb per day could easily add up to ~150 mb in a month.

I think only headers are downloaded, so it shouldn't add up to that much. I don't know for certain, also maybe it depends on whether you use POP or IMAP.

I use push on my Gmail through Google Sync (IMAP), and don't have the kind of data usage OP does. I don't get a ton of email mind you, but am regularly receiving email throughout the day.
 
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