According to developers, regulations being enforced by the China Ministry of Industry and Information Technology, is prompting Apple to remove CallKit-enabled apps from the China App Store. (Apple's CallKit frameworks let voice-over-IP (VoIP) apps integrate into the built-in Phone app, from dialer to call history list.)

From 9to5Mac:

Apple has started sending notices to developers who offer apps in China with CallKit integration. The notice explains that apps cannot offer CallKit functionality in China due to government regulations. In order for developers to make their application available on the China App Store, they must remove that CallKit integration. Alternatively, they can remove the application from China altogether.

This is essentially the same story as Apple removing VPN apps from the China App Store. The Chinese government wants complete control over the internet and communications systems in the country and that means providing tools to shield activity, like VPN, or operate outside the traditional telecommunications system, like VoIP, are illegal.

In addition to VPN and VoIP apps and integrations, Apple has had to move iCloud data for Chinese citizens to Chinese-based and owned data centers.

Apple can comply with those laws, break them and be forcibly evicted from China, or pull out of China unless and until those laws are removed. Historically and consistently, Apple has chosen to remain engaged with governments and in areas where it believes that engagement can help elicit change. That's true environmentally, politically, and socially.

What remains to be seen, specifically in China's case, is whether or not it can prove to be effective. Especially in the short term.