If you've got OFP: Resistance and are using OFP's new socket MP interface to connect to OFP servers, you'll need to use an external program for voice communications during MP gameplay.
For all older versions of OFP and for those continuing to use OFP: Resistance with the DirectPlay MP interface, you'll most probably be satisfied with OFP's own built-in Voice-Over-Network (VON) and text communication facilities.
Before you can use OFP's VON, you'll have to make sure that OFP can work correctly with your computer's microphone. To do this, run the OFP preferences program and click on the VOICE SETUP button. This will run a sound wizard test program. Follow the instructions carefully and, when completed, you should be all ready for VON communications.
Once you're connected to a host's OFP game server, you can begin communicating with other players. To begin, simply press the "/" key on your keyboard for text based communications. You can toggle voice communications on and off by pressing the keyboard's CAPS LOCK button.
When you first press the "/" key, you will, by default, be communicating on the GLOBAL channel. Messages on the GLOBAL channel are picked up by all players, including those on the opposing side. This is not a good channel to discuss your side's secret tactics and other hush-hush matters. Duh! So OFP offers you the following additional channels that can be cycled through by pressing the "," (comma) and "." (period) keys: