FaceTime, iCloud and iMessage in China Can one use FaceTime on an iPhone 6 without being billed international rates?

I have a iPhone 6 bought in U.S. and I am going to China to visit family for six weeks. The iPhone region is United states. Do I have to change my region on my iPhone while I am in China in order for my U.S. WeChat account to work? Or do I use the FaceTime or iMessage apps?
FaceTime, iCloud and iMessage are location-independent. The location of the sender or recipient does not affect the price you pay to use the service: free.

However, how you connect to the internet may cost. Using free Wi-Fi will be free, or you can pay roaming rates to your SIM card provider for cellular usage, or you can purchase a Chinese SIM card and pay a provider in China. This is payment for connecting to the internet, to use any service, not specifically for any Apple services.

You should not change your iPhone region.