Q:

I want to integrate the VOIP audio calling to my Android application

Is there any example of the voip integration to an Android app? 
I want to call audio connecting to the user just give me the example of the voip integration on Android and is there any another way to audio calling please give me proper guidance on audio calling integration. 

A:

I have tried and tested a sample application for app to phone calling.  Link here https://github.com/febimfelix/MyVoipCaller
I used sinch library.