There are some basic ways for communication between the two factions.
I recently made a mage on a new PvP server, and I joined a group for BFD. We didn't have the flight path yet, so we all had to walk there. The other 3 were in Ashenvale, and I was still in the Barrens.
From what I gathed in the party speak, they all happened upon a NE rogue around our level, and they all attacked it. The rogue took all 3 of them down.
They all ressed at the same time and tried again. They all died again.
By the time I got there, their ghosts were hovering over their bodies wondering what to do. I just sheeped the rogue, threw all my spells at it, froze, blink, threw some more, and they didn't res and join in till it was almost dead.
Anyways, you're wondering what relevance this has to this topic, right? Well, the NE rogue came back and ressed again, then it stealthed into the woods somewhere, we never found it. But it had a macro or something that it kept hitting that yelled in common "me love you" Well, that's what it looked like to the horde anyways. Also, it was oddly spaced... more like "m e l ov e y ou" or something.
So I guess there are ways of communication, but it probably takes so much time that it's not worth it.