Android running application in the background - Beginner

I am a beginner in Android development, and i need to know the following;

1. I need my application to operate in the background, even if th开发者_StackOverflowe user gets a call my application should run uninterruptedly. Can this be done ? I have heard that android only allows 1 application to run in a given instance

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To run code when your app is not in the foreground, you want to run it in a http://developer.android.com/reference/android/app/Service.html.