already using My Data Manager
Thanks for the tip - I was using My Data Manager - that's what told me that Contacts used 2.6 GB in one month. Unfortunately, that's not very specific. I think Contacts appears as the app name, but other things are inside it - including things like Google, Facebook and anything even remotely related to contacts - maybe even the Google+ service that uploads photos for all I know.
I tried another app and it gave me a little more detailed listing of Contact's inside apps, but still didn't say which app used which bandwidth, just gave a list of them with the big 2.6 GB at the top.
The good news is that it dropped in April and May, but still was 747 MB for what I consider "no reason".
It's funny - I went back to AT&T store and played with a Windows phone and with the old iPhone4 again (used to have one) and I found enough issues with every phone to know that I'm not happy with any of them. iPhone screen is too small after using an Atrix2, Windows doesn't so some things intuitively that others do, and with Android I just can't get it quite right - no app does what I want/need for the main functions (calendar, text, email, browser, keyboard). No keyboard app is as slick as the iPhone's was.