I've spoken with a few about having this feature on the server, while some say to use Skype it and those similar to it use far too many resources(processor, ram, bandwidth, etc.) especially for those with computers that are already pushing it to run minecraft. from what I've looked up mumble/murmer is a light app to use and can be integrated very easily into a server for just that servers use so no spamming. this would be nice especially with a community such as zedwork where there are so many people that do enjoy chatting with each other while playing but have to stop everything just to type...
this is just my thoughts on the subject as someone how would like to be more connected to the community and help to enhance the overall game play for everyone.