Hideo Kojima posted an interesting tidbit about Metal Gear Solid Peace Walker
on his development blog, helpfully interpreted here
. Apparently Snake/Big Boss has two methods of using the series' trademark radio, the CODEC. "Live" messages broadcast from HQ during the missions are played out while you're moving--you don't go into a separate screen while talking heads yak at you. This is done because the game has a strong co-op emphasis so both players need to progress during CODEC messages. While this is convenient it's also more realistic; in previous games, I wondered how Snake could stop, often in the middle of a firefight, and converse with his buddies for sometimes over a dozen minutes.
However, pre-recorded briefings given before the mission started are stored in your CODED for later review. This makes more sense--Snake would realistically get a lot of topographical info, intel and objectives before
he entered a mission area, and that's just the kind of info stored in the briefing files. I've been a Metal Gear fan since the original Solid on the PS1 and it's always interesting to see how Kojima and his team further refine the games in newer entries.