User blog comment:Bloodmanex/Voice chatting in multiplayer acr/@comment-5088097-20120921162332

By leaving them a PM? If you have Xbox 360, just add them and leave them a message by pressing the Xbox Guide button. The same applies for Playstation 3 users... If you're referring to talking to them while there is an online session as in... verbally communicating... then I am sorry to tell you that there is no such feature.