Hello,
I am one of the maintainers of the Linphone PPA. I have not packaged version 3.6 because the
Debian VOIP Team, of which I am not a part, started packaging Linphone for Debian. Their packages eventually propagate to Ubuntu and render our PPA less relevant.
If you have an urgent need for the latest version, you can use the official Debian package (or one from our PPA) to generate a binary package for version 3.6. I would be happy to answer questions to that regard, if you have packaging experience.
In addition, I will consider packaging 3.6 for the people on this list, if there is overwhelming demand or a good reason (such as security) why people must move to the new version immediately.
Felix