Hold the back button, press whatever button Crytek decides to initiate the vote, and others can jump in the same way and complete the vote. But be notified on screen just like PC of said votes.
And text chat.
For those of us with one of these: http://www.xbox.com/en-US/xbox360/accessories/headsetscommunication/Xbox360Chatpad
Or a USB keyboard connected to their system, can use text chat in game.
I know there's voice, but sometimes I really don't feel like messing with my mic setup.