Android : how to get the exact date of the last call in android?

I have my android app with Edittext , Button

Edittext : to allow the user to enter the number he wants . Button : called "Call" to make the call .

and i want a way to get the exact date and time of the call after it finishes

my java code :

public String string; public String number = null; //

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
   Button CallButton = (Button)findViewById(R.id.button1);

   CallButton.setOnClickListener(this);


}

@Override
public void onClick(View arg0) {
    // TODO Auto-generated method stub

       EditText txtcallnumber = null;
       txtcallnumber = (EditText)findViewById(R.id.callEdit);
    string = txtcallnumber.getText().toString();
       number = "tel:" +string ;
    Intent CallIntent = new Intent (Intent.ACTION_CALL,Uri.parse(number));
    startActivity(CallIntent);



}

how can i do that ?

thanks in advance