How to create a service for my application?

I'm building a SIP application, it works well now, and i want it to stay working as service when quit it to always receive incoming calls(to quit completely the app, the user has to confirm it by tapping "Exit" in the menu option). How can i do 开发者_StackOverflow中文版it ? Thank you very much for your help.

Well you could start by reading the documentation: http://developer.android.com/reference/android/app/Service.html

That has various sample code for writing services. Look at ApiDemos for more sample code.