I'm like 98% sure that Sony and Microsoft both give very good documentation and the like in SDKs on how to set up in-game chat. I'm also pretty sure it happens over those networks, not the server in the game. If there's one system it might be an issue on, I assume it'd be the PS3, since they never had a 'party chat' system of any sort, but plenty of devs for multiplayer components incorporated chat into PS3 games. Honestly, the only MP game I can think of without it is Journey.

[quote]I'm sure they have plenty of ideas on how they want it to work, but programming is most likely the issue, or possibly the servers could be the problem, The servers simply might not be capable of handling voice chat.[/quote] Sadly programming has nothing to do with it. Some sort of easy access to communication was the number 1 gripe from both alpha and beta. Activision put their foot down and said "No! We dont wanna! We think all our customers are 12 year olds!" The voice system could be taken from halo by literally copying and pasting in the code. Then you just have to bind it to a key. This should technically be very easy to implement.