I hope you guys are still rolling on this project, it sounds awesome. I have been thinking about the radio. It is simple, but very powerful. It could build tension, be a method to give 'hints' (which is just motivational info),moderate the timeline of the mission, and just plain nudge the player to do your bidding (more subtle than a piece of text or a change of objectives).
Also, (not sure how realistic this is) have multiple freq's to try contacting naval, air, and close inf groups to join up, or request support. If you can make contact, the party on the other end of the line will try to arrange evac... it might take some time, while you're waiting, could you call in that pesky milita HQ for bombardment? or give the player a coord for shore pickup, or give info on enemy/friendly activity. either way trying different freqencies would allow for more options on the radio. new menu options and such.
Examples:
1. Build tension -
When the player wrongly tries to make contact (wether it's too early, wrong position, just not time to finish mission, etc.), Have a few low bitrate recordings of a choppy, static filled message where the only clear part is to change position and try again "You're bre..(static) Signal wea... get to hi.. ground and try again.. we.. located at...." this will help motivate them to move around and not camp.
Also, getting emergency chatter from local troops being attacked would add atmosphere, and hope. Imagine, you hear faint requests for help over the radio, amidst gunfire, of course, and one of your troops says (text) "I have their position, its.. (variable for map position of just spawned friendly and enemy units)" you might be in time to help, or join up, or stay clear of activity.
2. Give Hints - You Radio your status.. Low ammo, injuries. Based on the (now known) random factors in the mission, the contact you have might be able to mention that: a group just cleared this village and there was a medical facility, or there was a battle at this position-scavenge weapons and ammo. (all spawned as needed by the master random event script).
3. Adjust Timeline: Being full of options, and as you already stated, a good amount of randomness, the radio might be found and conditions favorable to use. And barring the set time-of-activation I read about earlier, you might consider having problems that actively get in the way and need to be solved, or circumvented to complete the mission. (in other words, 'storied' excuses to extend the time of the mission)
This just inspired me for some ideas on a seperate thread. Thanks, and good luck. Sounds like you guys have a masterpiece in the works!
Scrub