How to intercept and parse incoming calls via an app

Question

How does Truecaller intercept incoming phonecalls on the iphone to display caller ID?

I didn't think this was possible from within the app?

Specifically, if I wanted to build this functionality, what protocols would I go about using?

http://www.truecaller.com/how-it-works

Answer 1

 On an iPhone, without jailbreaking it:
    - you cannot intercept a call in any way
    - you cannot determine the phone number nor the caller ID identifying information regarding the call. Even if you could there
    is no way to alter what is displayed on the call screen
    - you cannot block the call
    - your program can get a notification when a call is being made/terminated etc. But only if your app is executing in the
    foreground at the time of the call or if the app is in the
    background and has a relevant background mode (even then you can
    only know there is a call in some circumstance, depending upon what
    you're doing in the background and what state your in etc. Its too complex to describe the exact situation here briefly)

Answer 2

True Caller doesn't do that on iOS as it isn't supported with the native SDK. See their FAQ:

http://www.truecaller.com/support , specifically the "Why don't I receive live caller ID?" Section under "iPhone/Windows Phone". If you must though, try looking into a solution for jailbroken devices.

Answer 3

It's impossible to "intercept" calls. It is possible to handle the "background event call" when a iPhone get's a call. That said, Truecaller doesn't intercept calls. More info can be found on their website.