You can try to enable it with a code, Google it!
My carrier doesn't support volte so i couldn't try if it's really working when it is enabled
*Edit* Here is what I found:
VoLTE for other countries has been disabled. If you want to enable VoLTE, dial *#*#86583#*#*. But all the risks are borne by the user. We do not guarantee that VoLTE feature will work properly after you enable it. This solution is temporary. VoLTE will be enabled in the future based on related test results