Implements hook_form_FORM_ID_alter().
Add the default personal contact setting on the user settings page.
function contact_form_user_admin_settings_alter(&$form, &$form_state) {
$form['contact'] = array(
'#type' => 'fieldset',
'#title' => t('Contact settings'),
'#weight' => 0,
);
$form['contact']['contact_default_status'] = array(
'#type' => 'checkbox',
'#title' => t('Enable the personal contact form by default for new users.'),
'#description' => t('Changing this setting will not affect existing users.'),
'#default_value' => variable_get('contact_default_status', 1),
);
}