You have just described ADS-C (Automatic Dependent Surveillance - Contract) part of the FANS 1/A suite of capabilities. ADS-C allows airline ops, ATC or any other agency in the ADS-C list to request GPS position and time, flight level, speed, climb rate, turn rate and often an abbreviated future trajectory from the FMC. This is done either as a one off request or as a 'contract' for reports at intervals, at waypoints, or changes in flight level or all of the above.
See section 2.2.6 in Global Operational Data Link Document (GOLD) (
http://www.icao.int/APAC/Documents/e...D_2Edition.pdf )
Around 50% of widebodies have this fitted already and it will be mandated in the near future for oceanic flight. This is what INMARSAT is now saying it will provide 'free' as a tracking service.