Party Chat option not available.
NeoGaf

Do you like to use the party chat option on your Xbox 360? Well, if you do, you may soon find yourself being forced out of using that option. Microsoft appears to be offering developers the option to negate the private chat option the Xbox 360 offers. Currently, players have the option of forming a private chat with players, but that will soon change.

Call of Duty: Modern Warfare 2 will force players to decide whether or not they’ll play the game and join the game chat, or choose to stay in a private chat and not play in the multiplayer game. With titles like Gears of War, Call of Duty: Modern Warfare, Call of Duty: World at War, and many other online based multiplayer titles, the private chat feature became a way of telling other players of enemy locations after being killed.

Such a feature shouldn’t detract from the overall online experience much, but there will surely be some gamers who won’t like the type of feature being implemented. With some gamers only using the private chat to talk to friends while playing different games, this will likely pose a problem for them.

Source; http://www.examiner.com/examiner/x-12218-Providence-Video-Game-Examiner~y2009m11d1-MS-forcefully-removes-party-chat-for-upcoming-titles 

EDIT:

• Mercenary Team Deathmatch
• Free-For-All
• Third Person Teams

• Domination
• Ground War
• Demolition
• Sabotage
• Headquarters Pro
• Search & Destroy
• Hardcore Search & Destroy
• Capture The Flag
• Team Deathmatch
• Hardcore Team Deathmatch
• Third Person Cagematch

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I don't know why MS would do it, and i highly doube that they will. And if the reason would be that people tell where enemies are in multiplayer games after they're dead, its just silly. The whole purpose of being able to talk to eachother while playing multiplayers, is to alert your allies to where the enemies are. I mean just look at the competetive PC e-sport scene with ventrilo etc.

Any thoughts to why this would happen? It can't be to save the few by ruin it for the many! Cost? Doubt it. Even true? Unlikly. Just for MW2? Dunno!

It makes sense for games like Call of Duty

That will be a problem or ill just be muting a lot more often.

^^But it dosen't make sense for CoD? Competetive gaming and the entire e-sport scene uses some form of chat to perfect teamplay. Even after they're dead. I can only think of CS where ones screen goes black after you get killed. So that you cant help in calling out enemy positions.

But to alert someone that he who killed me was in a certain spot when it happed really dosen't help much, unless that guy is camping in the same location. But then it would probably be a public game, and in that case, that guy just had it coming. And there's really no need to take such actions just to make sure that a public game is "fair".

But then again, this is the new CoD. And i wouldn't be surprised. But as for PCs, its not like they can stop people from using 3rd party devices like Vent.

Does PS3 even have Party Chat? Why does it bother you so much? ~_n

If this is true I will have no reason to continue with live. Love to talk to friends as we play differant games. Get tired of talking to annoying and hateful people in the open chat all the time. This is truefully about the only feature of gold I really value. Bullshit in its fullest if this happens.

Is that going to change when you play on your PS3, which also doesn't have Party Chat?

I like, if they take it away i may just quit paing for live!

^ I doubt it will be removed completly, but like they said (if true), that MS has given developer the Option to exclude it. But i think everyone, well most anyway, see the upside of party chat.

So i think its more software related (games) than Live itself.

ROTFL! +1.