While I do like the general idea of the chat channels that LUKENBACHER suggested, this brings up the issue that people who play alone, and join a room where a lot of people in the same clan are playing. The person who is playing alone might be left out of the conversations and strategies that the people who are playing as a group in a different chat channel are having.
This sparked my own thoughts about how I think the SOCOM 4 voice chat system should work. This harkens back to an idea I was pushing on Slant Six before SOCOM Confrontation and has to do with the PS3 launch title Resistance.
Insomniac (developer of Resistance) was very progressive in terms of Resistance's online interface and how the various systems worked together to encourage a team environment that I think the game pulled off very well, particularly the chat system.
All the separate chat channels were open mic, but the main channel you had to press and hold a button. And even if you were in a separate channel you could press and hold that chat button to talk to everyone on your team, regardless of what channel they were on. So people in the main chat channel/other channels could still be privy to strategies and still communicate with people in other chat channels by holding down a button.
I think this is the absolute best way to execute the chat system, and encourages teamwork not only between clans, but between lone rangers and strangers (hey, I can rhyme) as well.