First time I took Galaxy 5S to China. I used to take my Motorola DREOID RAZR MAXX and it worked fine. I don't have a Global Plan, I just pay as I go because I don't need to use much and I keep Mobile Data off. I have the Network Mode set to Global. I tried CDMA and didn't have an effect. I have restarted the phone a few times to re-establish connection to towers.
I can send and receive text messages just fine. I can also RECEIVE phone call. I cannot PLACE a phone call. I'm dialing 00 1 xxx xxx xxxx