Our group began flying cooperatively in the days prior to voice comms. This presented HUGE challenges:
1. Meeting online pregame.
2. Communicating pre-flight (before entering the mission).
3. Communicating during the mission.
4. Communicating post-flight
And, if connection was lost by any player (remember, these were the days of dial-up connections for most people), communicating with those still inflight while you sat at desktop trying to figure out why your game crashed.
We used ICQ, server lobby text chat and ingame text chat, but these solutions were less than ideal.
Voice comms solved those daunting problems.
No, having "radio comms" is not realistic, but when I sit in front of my computer here in Hawaii, and fly with others half a world away, hand signals are bit hard to interpret