I think they should add an in-game voice chat function.

Here's how I think it should, and possibly could work:

If your solo and wandering around town or the forests -> You can only respond and read text.

However, if you have your LS turned on, Free Company active, or in a party, there should be a toggle or menu option, or button to start and/or join party chat function for PS3 players to communicate with each other and their PC counter-parts.

For PC players that don't have mumble installed, or Ventrillo, they can use it to, but most likely, if they already have them installed, like me and everyone else mostly does, they can continue to keep on using them.

I don't know the technicalities of how to make this kind of stuff actually happen, but I really enjoyed using it on FF XI when I played with my cousins or friends through Xbox Live party chat. So, if I didn't have that then the game would have sucked ass for me, since it was my first Final Fantasy and talking to others through chat really helped me learn about the game and connect.

It's not 100% needed, but I honestly do feel that it should be strongly considered sometime down the road for future players.