Several major HD radio broadcasters have agreed to allow iTunes tagging, which lets listeners mark a preview of a song they hear on an HD receiver for purchasing. CBS (NYSE: CBS) Radio, Clear Channel (NYSE: CCU), Cumulus, Cox, Entercom and Greater Media are currently in the process of installing iTunes Tagging technology on their HD broadcast systems. HD radio developer iBiquity Digital has been working for the past few months to secure the agreements among Apple (NSDQ: AAPL) and the broadcast groups. Last week, it signed a deal with Ford, which has promised to make HD radio available across all of its product lines. There are roughly 1,500 U.S. HD Radio stations are on the air and the system is now being tested in over a dozen countries, including Australia, Brazil, Canada, Czech Republic, France and Hong Kong. Release