This is a new feature for Windows Phone 7. An API will be provided for external services to validate that a call is coming from a Genuine Windows Phone. This will be accomplished by a requirement that every phone have a unique certificate applied during manufacturing process (similar to an IMEI, but more than a simple number, an actual .cer). The certificate is to be stored in the “Device Provisioning Partition” during the manufacturing process and is to be destroyed upon completion of manufacturing. Any time a reflash occurs, a new certificate is to be issued. This represents a significant change from the existing paradigm as your phone will be instantly uniquely identifiable through this method.