Ah yes - I understand what you're saying, but don't just point out the good stuff. Integrated also means:
1) A whole 'nother layer of difficulty in the game, one more thing to not work right. At least with the separate ones you can work out for yourself that you need to start one up first, need to adjust this, that, etc.
2) Yah, um... sure, with integrated voicecomm mod developers have yet another thing to figure out, lol - depending on how Epic coded it in, the option to disable some peeps from talking to others may not even be feasible.
3) Who's gonna write it? As things stand now, all you could really do is incorporate a 3rd party program, and that means someone paying someone else - AND you're back to where you were with compatibility.
4) This'll never happen for UT - Epic has stated many times that there aren't going to be any more patches, let alone a whole 'nother coded part!
From where I stand, this needs to be done in the NEXT level of Unreal, U2 or UW. And then integrate the snot out of it, so that it has many, many options and is flexible enough so that mods can change what they need. It also needs to be FULLY integrated, so that if the game runs on a platform, it just simply WORKS - BUT, keep in mind that voicecomm requires MORE from the server - more bandwidth, more CPU - so it should also be able to be turned off by server admins, or, better yet, server admins should be able to choose where the voicecomm 'base station' resides - then you could use someone else's or run yours on another box.