One of the good things about SH IV is the appearance of the radio option. It's a superb addition as far as historical immersion is concerned and has been well developed by CaptainCox and Tedhealy, among others.
Several people, I believe, have looked at the possibility of incorporating something similar into SH III, but have come up against the problem that the radio appears to be hard-coded into SH IV. The Sound.act file in SH IV is very different from the corresponding SH3Sound.act file.
Even in SH IV there's a problem with "scripted" radio programmes ( i.e. programmes which play at a certain time on a certain date ). If you save a game, when you resume, the radio begins to play programmes from the date and time the mission, started, not the point where you left off.