We have just added a new field to the XML response that is provided when using the "Advanced Method" API. This new field is labeled, "Bandwidth_Remaining", and it will report the bandwidth remaining, in Kilobytes (Kb), for your account through your next reset date.
We have also updated the associated XML Schema (XSD documentation) for those of you who require it for compliance or certification, such as using with SimpleXML.
NOTE: This new report will allow for more robust management of resources, by way of a greatly improved "Sample Code" that we will be announcing soon. It will also allow us to move to the next stage of our pricing model (eliminating "new requests"), when we finally get to that point.