This is exactly what is done in Australia for the 2 major football codes by the ABC (Australian Broadcasting Corporation which is government owned). The Grand Finals and held on consecutive weekends and Triple J radio (a part of the ABC) broadcast "The Festival of the Boot" pt 1 and 2 for the respective Grand Finals, which provides a comedic commentary about the game. It is broadcast across the country. There have been famous names introduced into the Australian vernacular from these broadcasts including "The Brick With Eyes" a current Australian Senator (https://www.google.com/search?q=brick+with+eyes&ie=utf-8&oe=utf-8)
The technology they are using is called cell broadcast and has been around as long as GSM. Emergency services in Australia use it for bushfires etc in order to notify residents they cannot in other ways. As for the mask issue, it is probabaly an attempt to stop them wearing gas masks and make their tear gas attempts more effective. Some of the latest action can be seen here http://www.youtube.com/watch?v=cuO53xeZkm8 if you like to see police/military dodging molotovs not so successfully.