Android应用中怎么实现一个通话录音功能

package com.eboy.phoneListener;
import java.io.File;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.media.MediaRecorder;
import android.os.Environment;
import android.os.IBinder;
import android.os.Vibrator;
import android.telephony.PhoneStateListener;
import android.telephony.TelephonyManager;
import android.widget.Toast;
public class phoneService extends Service {
  @Override
  public IBinder onBind(Intent arg0) {
    // TODO Auto-generated method stub
    return null;
  }
  @Override
  public void onCreate() {
    // TODO Auto-generated method stub
    super.onCreate();
    TelephonyManager telephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
    telephonyManager.listen(new PhoneListener(), PhoneStateListener.LISTEN_CALL_STATE);
  }
  private final class PhoneListener extends PhoneStateListener{
    private MediaRecorder mediaRecorder;
    private File file;
    private Vibrator vibrator = (Vibrator) getSystemService(VIBRATOR_SERVICE);
    @Override
    public void onCallStateChanged(int state, String incomingNumber) {
      try {
        switch (state){
        case TelephonyManager.CALL_STATE_RINGING: //来电
          break;
        case TelephonyManager.CALL_STATE_OFFHOOK: //接通电话
          file = new File(Environment.getExternalStorageDirectory(), incomingNumber + System.currentTimeMillis() + ".3gp");
          mediaRecorder = new MediaRecorder();
          mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
          mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
          mediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
          mediaRecorder.setOutputFile(file.getAbsolutePath());
          mediaRecorder.prepare();
          mediaRecorder.start();
          Toast.makeText(getApplicationContext(), "电话已接通，开始录音。", Toast.LENGTH_SHORT).show();
          //震动一下
          vibrator.vibrate(100);
          break;
        case TelephonyManager.CALL_STATE_IDLE: //挂断电话
          if (mediaRecorder != null){
            mediaRecorder.stop();
            mediaRecorder.release();
            mediaRecorder = null;
            Toast.makeText(getApplicationContext(), "电话已挂断，录音停止。", Toast.LENGTH_SHORT).show();
            //震动一下
            vibrator.vibrate(100);
          }
          break;
        }
      }catch (Exception e) {
        e.printStackTrace();
      }
    }
  }
}

package com.eboy.phoneListener;
import android.content.Context;
import android.content.Intent;
public class BroadcastReceiver extends android.content.BroadcastReceiver {
  @Override
  public void onReceive(Context arg0, Intent arg1) {
    Intent service = new Intent(arg0, phoneService.class);
    arg0.startService(service);
  }
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.eboy.phoneListener"
  android:versionCode="1"
  android:versionName="1.0">
  <uses-sdk android:minSdkVersion="7" android:targetSdkVersion="15" />
  <application android:label="@string/app_name"
    android:icon="@drawable/ic_launcher"
    android:theme="@style/AppTheme">
    <service android:name=".phoneService"></service>
    <receiver android:name=".BroadcastReceiver">
      <intent-filter >
        <action android:name="android.intent.action.BOOT_COMPLETED"/>
      </intent-filter>
    </receiver>
  </application>
  <!-- 读取电话状态权限 -->
  <uses-permission android:name="android.permission.READ_PHONE_STATE"/>
  <!-- SD卡读写权限 -->
  <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
  <!-- 录音权限 -->
  <uses-permission android:name="android.permission.RECORD_AUDIO"/>
  <!-- 震动权限 -->
  <uses-permission android:name="android.permission.VIBRATE"/>
</manifest>