GUI Interface class

Hi, I’m trying to make a method that makes a call from a Mobile Phone class which should be a functional button in a GUI. When the phone number and the duration of the call are entered in the GUI,the method to get the display number is called and its value is checked. Anyone got ideas on how to write the makeCall() method? So far I’ve done this -

 public int getDisplayNumber()
{
    int displayNumber = -1;

    try {
        displayNumber
          = Integer.parseInt(DisplayNumberTextbox.getText());
        if(displayNumber < 0) {
            JOptionPane.showMessageDialog(frame, 
               "Please enter a positive number");
        }
        else if(displayNumber > numberOfGadgets()) {
            JOptionPane.showMessageDialog(frame, 
               "Please enter a number in the correct range");
        }
    }
    catch(NumberFormatException exception) {
    }
    return displayNumber;
}

 public void makeCall()
{
    int displayNumber = getDisplayNumber();
    MobilePhone mobile = (MobilePhone) item.get(displayNumber);
}