Conversation Mode Tone Alerts

I set the tone I want for text messages but while I'm in that message or conversation, I don't need the tone to keep beeping everytime the other person types a message. I'm still in the same conversation and it gets annoying.

Any way we can have a different tone set just for additional texts while I'm still in that same conversation?

The Nokia N900 is like the only phone I know of which does this and I freakin loved that feature! Made it easy to conversate with your friends without the constant beeping or message alert you have.

There may be an app for that somewhere... but you certainly can't do it by default

If someone can provide the name of that App that would be great!