Modifying existing built-in phone application

Question

Instead of building my own custom telephony application by making use of the TelephonyManager class, is it possible to modify the built-in native phone application on a Google Nexus 4 or 5 device to make it do what I want?

Answer 1

You can get the source code for the system apps (for example, the Dialer app is at https://android.googlesource.com/platform/packages/apps/Dialer/) and then modify it or use it as an example.

http://source.android.com/source/building.html might be useful to set up your dev environment to get the code.

Also, see Download and modify android core apps in eclipse