According to TrackingtheWorld press release:

The United States Postal Service (USPS) processes and delivers more than 212 billion pieces of mail per year to Americans. The U.S. Postal Service continually aims to increase its quality of service, to reduce delivery times, to pinpoint logistical inefficiencies, to save costs and to eliminate waste.

To support this challenging task, the USPS commissioned TrackingTheWorld Inc., a leading global positioning technology firm, to develop a letter-tracking GPS device that would meet the agency’s precise needs.

These needs include reporting the positioning of letter mail from anywhere on the planet at customizable time intervals, interfacing with Google Earth, and recording down time, all fitted in a device conveniently and completely unnoticed within a standard size envelope

Scheduled released February 1, 2008