Excuse me, what is free of charge?

Incoming call do not disturb means the same as "do not disturb mode", that is, use the software that comes with the mobile phone or provided by a third-party software provider to block the short messages and incoming calls of people who don't want to see it.

Sometimes, in order to prevent the interference of external information, you can turn on incoming calls to block all incoming calls, which is a bit like airplane mode, but the difference is that you can receive text messages or incoming calls from some people.