how to fix this code to enable the back button
<p>This is a phone app project for android. I need to enable the back button during the call, so how to fix this code to enable the back button during the call?</p>

<pre><code>    public boolean onKeyDown(int keyCode, KeyEvent event) { //to enable the back button
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            moveTaskToBack(true);
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button b = (Button) findViewById(R.id.button);
        b.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                mTelMgr.listen(mListener, PhoneStateListener.LISTEN_CALL_STATE);
                callIntent = new Intent(Intent.ACTION_CALL, Uri
                        .parse("tel:006599"));
                startActivity(callIntent);

               onKeyDown(0, null);      // call the method  

            }
        });
        mListener = new CallEndedListener();
        mTelMgr = (TelephonyManager) this.getSystemService(TELEPHONY_SERVICE);
        onKeyDown(0, null);    // recall the method
    }
</code></pre>
