I’m sure D3 has a built in chat feature without needing a 3rd party software – but it’ll likely be limited to the 4 players in the game. Most games end up with their guild/groups on Ventrillo or Teamspeak, depends how many people play together really, and whether or not D3 allows for channels/chats based on b.net battletags rather than only those in the instance, we’ll find out soon!