PhoneStateListener
1.對特定的電話狀態的監聽，包括服務的狀態、信號強度、消息等待指示（語音信箱）、通話轉移、呼叫狀態、設備單元位置、數據連接狀態、數據流量方向。一些電話信息受權限保護，應用程序不會收到受保護的信息的更新，除非在manifest文件中有適當的權限聲明。凡申請許可，有適當的LISTEN_標志。

2.對監聽的話做處理
Handler mHandler = new Handler() {
   public void handleMessage(Message msg) {
       switch (msg.what) {
           case LISTEN_SERVICE_STATE:/*Listen for changes to the network service state (cellular).對網絡服務狀態監聽*/
              PhoneStateListener.this.onServiceStateChanged((ServiceState)msg.obj);
              break;
           case LISTEN_SIGNAL_STRENGTH:/*Listen for changes to the network signal strength (cellular).對網絡信號強度變化監聽*/
              PhoneStateListener.this.onSignalStrengthChanged(msg.arg1);
              break;
           case LISTEN_MESSAGE_WAITING_INDICATOR:/*Listen for changes to the message-waiting indicator.對消息等待指示的變化監聽*/
              PhoneStateListener.this.onMessageWaitingIndicatorChanged(msg.arg1 != 0);
              break;
           case LISTEN_CALL_FORWARDING_INDICATOR:/*Listen for changes to the call-forwarding indicator.對通話轉移指示的變化監聽*/
              PhoneStateListener.this.onCallForwardingIndicatorChanged(msg.arg1 != 0);
              break;
           case LISTEN_CELL_LOCATION:/*Listen for changes to the device's cell location. Note that this will result in frequent callbacks to the listener.對設備單元位置的變化監聽，這會導致頻繁的監聽回調。*/
              PhoneStateListener.this.onCellLocationChanged((CellLocation)msg.obj);
              break;
           case LISTEN_CALL_STATE:/*Listen for changes to the device call state.對設備呼叫狀態的變化監聽。*/
              PhoneStateListener.this.onCallStateChanged(msg.arg1, (String)msg.obj);
              break;
           case LISTEN_DATA_CONNECTION_STATE:/*Listen for changes to the data connection state (cellular).對數據連接狀態的變化監聽。*/
              PhoneStateListener.this.onDataConnectionStateChanged(msg.arg1, msg.arg2);
              PhoneStateListener.this.onDataConnectionStateChanged(msg.arg1);
              break;
           case LISTEN_DATA_ACTIVITY:/*Listen for changes to the direction of data traffic on the data connection (cellular).對數據流量移動方向的變化監聽*/
            PhoneStateListener.this.onDataActivity(msg.arg1);
              break;
           case LISTEN_SIGNAL_STRENGTHS:/*Listen for changes to the network signal strengths (cellular).對網絡信號強度的變化監聽*/
              PhoneStateListener.this.onSignalStrengthsChanged((SignalStrength)msg.obj);
              break;
      }
   }
};

3.監聽變化后發送消息
IPhoneStateListener callback = new IPhoneStateListener.Stub() {
    public void onServiceStateChanged(ServiceState serviceState) {
        Message.obtain(mHandler, LISTEN_SERVICE_STATE, 0, 0, serviceState).sendToTarget();
    }
    public void onSignalStrengthChanged(int asu) {
        Message.obtain(mHandler, LISTEN_SIGNAL_STRENGTH, asu, 0, null).sendToTarget();
    }
    public void onMessageWaitingIndicatorChanged(boolean mwi) {
        Message.obtain(mHandler, LISTEN_MESSAGE_WAITING_INDICATOR, mwi ? 1 : 0, 0, null)
                .sendToTarget();
    }
    public void onCallForwardingIndicatorChanged(boolean cfi) {
        Message.obtain(mHandler, LISTEN_CALL_FORWARDING_INDICATOR, cfi ? 1 : 0, 0, null)
                .sendToTarget();
    }
    public void onCellLocationChanged(Bundle bundle) {
        CellLocation location = CellLocation.newFromBundle(bundle);
        Message.obtain(mHandler, LISTEN_CELL_LOCATION, 0, 0, location).sendToTarget();
    }
    public void onCallStateChanged(int state, String incomingNumber) {
        Message.obtain(mHandler, LISTEN_CALL_STATE, state, 0, incomingNumber).sendToTarget();
    }
    public void onDataConnectionStateChanged(int state, int networkType) {
        Message.obtain(mHandler, LISTEN_DATA_CONNECTION_STATE, state, networkType, null).
                sendToTarget();
    }
    public void onDataActivity(int direction) {
        Message.obtain(mHandler, LISTEN_DATA_ACTIVITY, direction, 0, null).sendToTarget();
    }
    public void onSignalStrengthsChanged(SignalStrength signalStrength) {
        Message.obtain(mHandler, LISTEN_SIGNAL_STRENGTHS, 0, 0, signalStrength).sendToTarget();
    }
};