[Android] Phone State Receiver

ref.

http://stackoverflow.com/questions/5948961/how-to-know-whether-i-am-in-a-call-on-android/5949116#5949116

http://stackoverflow.com/questions/6729072/android-phone-state-in-broadcaster-reciever

http://developer.android.com/reference/android/telephony/PhoneStateListener.html#PhoneStateListener()

http://www.eoeandroid.com/thread-8994-1-1.html