Package twinkle, a sip softphone is not currently available in epel7.
Installing from source also fails, due to dependency "commoncpp2" missing from the repo.
another sip softphone sflphone is also dependent on the same "commoncpp2" library.
twinkle is not maintained upstream for a very long time. It has been - with great difficulties - preserved in functional shape by Kevin but I suspect it will never be branched for EL7 unless someone very active is willing to take care of it.
I for one am not going to maintain it, especially as I am not planning on using CentOS 7 any time soon. So I am sorry but I am going to close this ticket. If anyone is willing to take over the EL7 branch, (s)he is more than welcome to do it.
As of commoncpp2, please file a separate ticket.