The fix I posted in another thread for getting VOIP to work seems to work, just tested it out now and I could be heard, so I thought I'd post it here for a bit more prominence as voice can be so useful in this game.

http://forums.electronicarts.co.uk/battlefield-bad-company-2-pc/947680-possible-voip-fix.html

Basically if you're using headphones just go into your settings file and change the speaker count from 0 to 2...easy peasy