I recently added an iphone to my account and the data usage summary says 650MB, however when I look at the detailed usage it says 2GB (which matches what the phone's tracker says). When I look at my other two lines the summary and detailed info is accurate (both android). Why is this?
Is it a new line, or just a new phone? For new activations the first ten days of data are usually zero rated, which means that the first ten days of usage wouldn't have counted toward your monthly limit.