I want to use one GB monthly. Set billing so that it does not go over
I was looking to do the same when I signed on with SM 8 months ago, can't be done. The only thing you can do is setup a "Data Notification" alert, however it will not prevent you from going over the 1GB $14 plan.
the one thing that you might do is go through your phones menu and look for mobile data and just turn it off and just run off of wifi hot spots