Originally Posted by bmwhd
Never mind, VOX apparently only works for phone calls.
For intercom sessions, the way it works is that once you have paired your two F4 units (rider/passenger), either of you can initiate an intercom session by pressing the MFB and holding it for 3 seconds. So in your scenario she would press and hold her MFB for 3 seconds, you'll both hear a beep, your music will pause and then you will hear her talking and you can talk back (full duplex). Unlike an incoming phone call, I don't believe there is a way for you to 'reject' an intercom session initiated by her.
This has been the biggest negative about the F4 that I read when I read the manual. My wife and I currently have the Scala Q2's and although we tend to "manually connect" if we are going to be talking for a while, its nice to have the option to open a conversation via Vox just to say something. My biggest concern with the F4 is the fact that you have to actually hold the MFB button down for 3 seconds to establish a conversation. I would have been more eager to over look the no Vox on the F4 if it was just a quick button tap on the MFB like it is on the Scala's, but I think having to hold it down for 3 seconds really shows they put the bike to bike communication behind the phone priority. IIRC, if you don't hold the MFB button down long enough, it tries to establish a voice call on your cell. I just think that would be super annoying if you screwed up when you really wanted to quickly relay something to your riding partner and instead of opening a conversation, you get the voice dial on your phone!
I guess I'd have to try it real world to see, but I think the potential is definitely there to be a super annoying quirk.