For Olympus Burning, I've been preceding each voice message with an appropriate "beeping" noise (much like that of FS1). It's easy, simple, and adds effect.
Though FS2 didn't use them, my campaign is bringing them back, all of them will end up being custom. I find that adding a beep before each message is sent tends to get my attention and have me listen more to the speaker in the midst of combat--so that if any details come up, it ensures that I get them on the first playthrough of each mission.
I use the FS1 "static" noise at the end of each message, because it's better than anything I could probably do in Audacity, and most genuine FreeSpace fans will recognize it.
What's you guys' opinion on using message beeps? Do they add effect, or are they just an annoyance?
Additionally, do you guys think they should they be optional?