Hey Hydra, I know you cant speak in game, have you checked all the permissions in gfwl? you could have some parental controls enabled by default, which might stop you speaking to strangers (which sounds weird, because the game lets you plow down hookers while drunk with your illegal immigrant cousin)
Press 'Home' to bring up the GFWL client and click on Account Management. This will minimize the game bring up the Xbox Live Management page in your web browser. From here, sign in using your Live account, then click on Privacy Settings. In the Text and Voice Chat section, make sure that it is set to 'Everyone'. Then 'Save', exit the browser and continue the game.
^thats for xbox, probs similar for pc.