在清单文件AndroidManifest.xml中添加权限：
    <uses-permission android:name="android.permission.READ_PHONE_STATE"/>
    <!-- 在SDCard中创建与删除文件权限 -->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <!-- 往SDCard写入数据权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.RECORD_AUDIO"/>
    <!-- 访问internet权限 -->
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>

public class PhoneListenerService extends Service {
@Override
public void onCreate() {
        TelephonyManager manager = 
                  (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
        //监听电话的状态
    manager.listen(new MyListener(), PhoneStateListener.LISTEN_CALL_STATE);
}

private final class MyListener extends PhoneStateListener {
    private String num;
    private MediaRecorder recorder;
    public void onCallStateChanged(int state, String incomingNumber) {
        switch (state) {
            case TelephonyManager.CALL_STATE_RINGING:  /* 电话进来时 */
                num = incomingNumber;
                break;
            case TelephonyManager.CALL_STATE_OFFHOOK: /* 接起电话时 */
                try {
                    File file = new File(Environment.getExternalStorageDirectory(), num + "_" + System.currentTimeMillis() + ".3gp");
                    recorder = new MediaRecorder();
                    recorder.setAudioSource(AudioSource.MIC);//声音采集来源(话筒)
                    recorder.setOutputFormat(OutputFormat.THREE_GPP);//输出的格式
                    recorder.setAudioEncoder(AudioEncoder.AMR_NB);//音频编码方式
                    recorder.setOutputFile(file.getAbsolutePath());//输出方向
                    recorder.prepare();
                    recorder.start();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                break;
            case TelephonyManager.CALL_STATE_IDLE:  /* 无任何状态时 */
                if (recorder != null) {
                    recorder.stop();
                    recorder.release();
                }
                break;
        }
    }
}
}