Visit Cato's site which has a Tribes2 Voice Communication manual that may be of help.  In addition the following was posted to the Tribes2 Official news page by [DEV] QIX

Many folks have been a bit confused about how to use the microphone with the game. Here's a quick tip on how to use it effectively:

1) Try your microphone outside the game first. Use SoundRecorder and make sure that you can actually record your voice properly. If you can, then your hardware is set up properly and you'll be able to use it in the game.

2) If you have a good bandwidth connection (cable modem, DSL, etc.) then turn UP the settings on your voice. The voice communication will be MUCH clearer that way. Try the v.12-v.29 setting, it works very well. Make sure to set both LISTEN *and* TALK settings.

3) Make sure you toggle "Enable Microphone" ON. And turn your input volume up to about 150-200%. Don't go too high though...your voice will distort a lot if you set it too high.

4) Make sure to use the Test Microphone button. If your voice doesn't sound good during the test, then it won't sound good in the game either.

5) Last tip...turn *down* your sound effects volume and crank UP your voice bind volume. That way, with your microphone at a good level, and your sound effects down, you'll be able to hear all the voice clearly in the game.

6) Oh yeah...MasterShredder reminded me...you can't use microphone communication if you're on-line using an alias. You can only use voice if you are using your primary warrior name.

The Dev Team does this all the time, and the difference that voice communication makes within a team game is truly phenomenal.