If it's for "excessive usage" then that number is less than 10MB per day. Since I first joined StraightTalk, my phone shows a total cellular usage of under 900MB. (I am usually on WiFi except, of course, when making phone calls or sending text messages - no MMS, of course.)
For me, this issue began yesterday (10/7/12). I have an iPhone 3GS running iOS 5.1.1.