private chat (aka cross-game chat), then get ready to be disappointed; I have no idea if/when this will be added
If it's any help, a Dev from naughty dog posted on a forum saying they didn't bother locking voice chat for dead people in Uncharted 2s last man standing mode as 'cross game chat is coming out in the next firmware update anyway so if people wanted to get around it they could'. The post was deleted shortly after it went up.
Whether there's any truth to that claim is another matter...


