Why does iPhone 6 remind Facetime to activate SMS charges?

When activated, data or text messages may be used, which is a reminder function to inform the user.

You can also turn off facetime in the settings.

The i-Phone4, iPhone4S, iPodtouch4 generation, iPad2 and ThenewiPad products produced by Apple all have Facetime and iMessage functions. Facetime is a free video chat software that connects any two Apple devices that support Facetime through a wireless network to achieve video calls. Facetime does not require setting up a special account or account name, and it is very simple to use. For example, if you want to start a video call with a friend, you only need to find her contact entry in the address book and click the Facetime button. Also, if you might be on a voice call with a friend and want to switch to a video call, just tap the FaceTime button on the phone screen. Using any of the above methods, an invitation will pop up on your friend's screen asking her if she wants to join your call. Once she accepts, the video call can begin.

iMessage is an instant messaging software in the iOS5 system released by Apple at WWDC2011. It can send text, pictures, videos, etc. between iOS5 and Macosx10.8 versions of Apple devices, and supports multiple To chat with others, users only need to communicate through wireless networks or 3G networks. iMessage also makes use of the new message reminder system of iOS5 and Macosx10.8, which can push information directly to the other party's screen, regardless of whether the other party is in the game or locked screen state. If both parties are using iMessage, there is no need to contact the communication operator. Pay any text message charges.