This guide is based on this article  found at www.linux-gamers.net.
Install the dependencies
Note: Make sure you have sqlite and/ or sqlite3 in your USE flags in /etc/make.conf, if you haven't emerged qt4 with these before, you need to reemerge it.
emerge dev-libs/boost media-libs/speex x11-libs/libXevie x11-libs/qt (See Note)
For Debian / Ubuntu
apt-get install qt4-dev-tools libqt4-dev libspeex1 libspeex-dev libboost-dev libasound2-dev libxevie-dev libxevie1
It's recommended to remove the package qt3-dev-tools if installed.
Download the source
Get the mumble source
svn co https://mumble.svn.sourceforge.net/svnroot/mumble/trunk mumble cd mumble/
Compile Mumble and Murmur (Mumble server)
qmake main.pro make
For using push to talk, edit /etc/X11/xorg.conf:
Section "Extensions" Option "XEVIE" "Enable" EndSection
Restart the Xserver.
For text-to-speech voices you will need to install festival and at least a voice. Most distros ship packages for that in their repositories.
cd release/ ./mumble
- see Running Murmur