You should install either My Data Manager or Onavo from the market and monitor your data usage with that. Either app will show you an app-by-app breakdown of what's being a data hog. Then you can investigate the settings in each app and plug up the leaks.
I would take these steps:
1. Open G+ and disable automatic upload.
2. Install My Data Manager or Onavo and set it all up to monitor your data usage.
3. Call T-Mo and ask to speak to tech support. (Don't tell them you using a custom ROM, if they ask you to go into About Phone and tell them the build number, say 2.3.4.) Tell them you just installed G+ yesterday and and it sucked you dry overnight. Let them know you plugged the leak, installed the data montioring app, and ask them for a one-time courtesy reversal on the data. They are pretty good about this, the tech guys understand that apps sometimes f--k us over.
Worth a try.
PS Believe me it won't be the stupidest thing the tech guy at T-Mo ever heard. They give out hella credits for dumber things than that. Just play dumb and don't act like a know-it-all, and they'll give you the credit and chalk it up to the Android learning curve.
Thanks man I appreciate the advice, I spike to tmo and they upgraded me to the 5GB plan just for this month, no reversal but oh well. But again thanks for yoir input.
Sent from my LG-P999 using XDA App