I read this article , it is good & clear.
But my clients are familiar with their mobile devices contacts built-in app.
I want in my app to call the mobile device default built-in contacts list, I want my client to search using it, and the result mobile number i should get it in my app through such an event or whatever.
You can use ContentResolver like i did it here for the Google Calendars.
The Device Contacts can be accessed in the same way.
Find the documentation here.
Speaking about the Calendars example (see above). The constants needed for the Contacts are in the Object "ContactsConstants".