VoLTE problem in custom rom [TURKEY]

I flashed Alexis Rom 5.2.1 and I cant find VoLTE option in phone app's settings . I think it's related to CSC thing , you know CSC . How can I use VoLTE ? I am waiting your helps .

Note: Also It was same in TYRANNUS ROM

from xda-developers http://ift.tt/28UFRUI
via IFTTT