The product folks are going to try and make a sanatized version of the feature list for 4.0(5) available - we'll post a follw up out here when they do.
I _can_ tell you, however, that broadcast messages will be supported (this is different than sending a message to a distribution list for those not familiar with the concept - these messages can force users to hear them, play first, etc...).
There will be a _limited_ ability to customize the key presses for the subscriber main menu, message playback and after message menus. That's it. You will not be able to simply customize the subscriber conversation any way you like it (I've had many folks ask for this - while a nifty concept, it's extremely difficult to develop and even harder to support in the field). You can map key presses for these 3 parts of the subscriber covnersation to existing functions we support.
Since I've gotten _so_ many questions about this (probably over 60 so far) I'm going to put a training video together and publish it early next week to actually show what it looks like to do this on a 4.0(5) beta box. I'll publish a link to it out here when it's ready to go - this should clear up what it is, how it works and what you can (and more to the point can't) do with it.
