Take on phantom usage

sometimes I just can't make sense of things... 

As a person who both travels internationally a lot and uses his cell-phone often, I'm keenly aware of the international data plans offered by the cell-phone companies and am very vigilant when using my allotted data.     This time before a 10 day trip, I signed up for a 125mb plan through AT&T for $49.99 which I figured should be more than enough being I used about 50MB the last time I made a similar trip but would always want to be safe and not feel limited as there are many dead hours in a day when checking in at home seems like the only thing you can do to keep yourself sane.     I reset the usage statistics on my IPhone 4 before landing in Asia and go about my normal business during a 2.5 hour layover in Shanghai.   When I get onto the next flight I check my usage and am stunned when it shows that I received about 7 MB but sent 136MB in the 2 hours I got to the airport eventhough I hardly used the phone since I was lugging my suitcase through the terminal, going through customs and finding the rest-room for most of the 2+ hours. 
Now I use on average about 600MB per month when state-side when I use my data-package without abandon since I have more than 2gigs per month at my disposal so the thought of having used roughly 1/4 of a 30 day period in less than 3 hours seemed ludicrous.  
I called AT&T and they confirmed the usage but could not state how it happened.   I assured them that I did not actively send out 136MB but that there might be something wrong with a setting.    Maybe there was something in an application which was constantly pushing out some data which some-how added up to 136MB but since this would also be occurring while I was home, this didn't exactly make sense.    In order to send out this much data I would have to send out about 70 high-resolution pictures and as you can only send out about 1 per minute it would have meant I spent nearly my entire time sending out pictures.
Anyway after 20 minutes, I am able to move to a 250MB plan although I'm still really shuked about this entire episode  mostly because there was a free WiFi connection at the airport....