Help Korean galaxy network problem

[ningistine]

Hello
normally my Korean galaxy is official releases since I tried it with both operator and it works (calls and internet and everything )but with the third operator there is a problem, sometimes it works and makes normal calls and sometimes it can not make calls or receive them knowing that the network signal is still good

 

[mikedt]

I know there's a mix of different network technologies used by carriers in South Korea, GSM/WCDMA and CDMA/EV-DO, as well as LTE. So if your phone is GSM/WCDMA only, it ain't going to be able to use the CDMA/EV-DO networks.