There is currently no TURN server available in Gentoo, as far as I (and eix) know.
https://code.google.com/p/rfc5766-turn-server/ is an example of one.
Created attachment 374814 [details]
ebuild draft for latest 220.127.116.11 version
needs still some work:
* enable examples USE flag
* bzip2 -d all examples and their relative docs
* bring postinstall.txt messages inside post_install()