Linphone 4.0 has been released a few months ago http://www.linphone.org/news/55/26/Linphone-4-0-for-desktop-platforms-is-available.html But it moved dependencies from gtk+ to Qt 5.9 which has no deadline for release in Gentoo.
Here we can monitor how the other distributions work on that https://repology.org/metapackage/linphone/versions
*** This bug has been marked as a duplicate of bug 504114 ***