13. The computer-readable memory of claim 10 wherein the stored usage data includes both aggregate usage data and incremental usage data, and wherein the aggregate usage data comprises cumulative usage data, and wherein the incremental usage data comprises usage data tracked since a most recent delivery of the message to the remote service.
14. The computer-readable memory of claim 13 wherein usage data accumulated following a delivery of a message to the remote service is marked as incremental usage data.