Where can I read about applications or functions that are prohibited from developing on IOS?

Question

iOS

Where can I read about applications or functions that are prohibited from developing on IOS?
I asked a friend a question about the possibility of developing one application for managing, expanding work with calls. He says it's forbidden. You can throw a link to the official development rules, I want to know if this is true or he decided to throw me and implement the idea himself, since it is very simple.

Answer 1

in app store rules

Answer 2

Look, it all depends on how you plan to distribute the application and monitize it
1) The light side of the force. Through the appstore. You are here https://developer.apple.com/app-store/review/guide... There are restrictions on both the api and what the application can do in general.
2) The gray side of power. Enterprise development. You can do what you want, distribute the application yourself, are untethered from the review team. but if apple notices that you are doing something bad, the certificates will be revoked and your application will stop working. It costs a little more
3) the dark side of the force. Cydia and jailbreak devices. You can do whatever you want) but there you will hardly be able to sell something. And the number of jailbroken devices is falling every year.
Your friend talked about points 1-2, but if you turn to the dark side ... In short, see for yourself

Answer 3

It's not about the rules, there is no allowed API for working with calls, so it's impossible. A friend told the truth