Things got quite weird as I and my app.net correspondents dug into this problem. See the updates below for the full story, which seems to have been a change in AT&T services that triggered a glitch in iOS cellular data controls just at the start of a billing cycle. A truly 21st century experience.
The messages started to appear around 3pm today ....
AT&T Free Msg: The following mobile ... has used 100% of the additional 200 MB of data ... We've added another 200 MB ... $15 will be charged to your account...
One after the other. They stopped at $136. Which AT&T, to their credit, forgave when I begged for mercy.
So what happened?
Well, to start with, our family is on legacy AT&T family plan contract that offered a low cost 200MB/month data plan option (as in this TidBITS article). It is a relatively cheap way to buy a subsidized phone -- $10/month for the voice, $15 for the iMessage-only data plan, low total cost of ownership. We did it 2 years ago before we switched #1 and #2 to H2O Wireless ($40/year, no data). That contract is up now and #3 is going to join her brothers in ultra-low-cost paygo land. Her 4S will need WiFi for data.
So it's easy to run through that plan. Except it shouldn't have happened so quickly. Take a look at the cellular settings for data in iOS 7 (see Update, wish I'd been more careful to include lower range in my screenshot):
Notice there's nothing there for Video or Movie? That's because iOS 7 isn't supposed to download movies from iCloud over a cellular connection. I tried on my 5s -- nope, not allowed.
But when I ran out to look at her phone I found she'd downloaded a 1.5 GB movie via cellular data. That shouldn't be possible, but there was a bug like this in iOS 6. (Note before iOS 7 this couldn't happen, a movie was either on the phone or unavailable.)
I think she started downloading the movie over WiFi, from the car in our driveway, at the very limit of our household WiFi. As she drove away her phone switched to LTE ... but the download continued.
It's just a theory -- but I'm betting that's what bit us...
- Serious iOS 7 Flaw with iTunes Match and Cellular Data - similar bug, but we don't do Match.
Update 11/29/2013: After writing the post below I found I could start streaming an iCloud movie on WiFi, then walk away from home until the WiFi died, and iOS 7 will continue streaming it over LTE. Which it's not supposed to allow. That's how my daughter ran up her bill.
Update 11/30/2013: This is getting weirder. In an app.net discussion @sirshannon sent me a screenshot with Videos as a cellular data option. I looked at my phone and there it was. I figured I was just demented, but @wickedgood sent a screenshot without the option and Emily doesn't have it on her phone ... yet ...
It's possible that AT&T is making network changes that enabled both my daughters download and, belatedly, this option. Or perhaps they've changed carrier settings -- though I thought that required a user action.
In the modern world, sometimes we're crazy and sometimes it's just reality flux.
Update 11/30/2013 b: Sure enough, this morning my daughter's phone also has the Cellular data control for Video.app (controls grayed out here as her cellular data is currently disabled).
She didn't have it last night, which was easy to tell as she has so few data using apps. I've since turned all but Mail.app off.
Update 11/30/2013c: Later in the day I was able to inspect the 3rd iPhone on our family plan. Emily's phone still does not have the Videos.app cellular data setting. Studying her phone I realized Apple had put some of its Cellular data controls in one settings menu (Cellular) and others in the iTunes & App Store menu (and some in both). At that point I had to laugh. These screen shots are worth a look...
First - no Videos.app control. I tried a few tricks that might "bring it on", including a power cycle, but nothing worked. I suspect it will appear tomorrow though.
Notice in her iTunes & App Store settings there's a special message. Her iPhone didn't, for some reason, see Cloud media, it's not fully associated with iTunes. I turned on automatic download for iBooks and, as you'll see below this message disappeared.
Take a look at these two screenshots from the iTunes and App Store config. There's an option to show or hide Videos that are in the cloud. That makes sense, but why the heck did Apple put a Cellular Data setting here?!
I tried downloading a movie from after disabling wifi (so this isn't yesterday's test, where I started the download on wifi then walked out of range) -
As expected. I'll check again tomorrow and report when her phone gains the Videos.app cellular data control.
What a mess.