Mobile number validation for webforms I am looking for a way to easily implement an Integer field with webforms that can do mobile number validation (US numbers only). I am aware of http://drupal.org/project/webform_validation that can do numeric validation but looking for a more direct solution. If its a hook, that works as well.
You can do a hook_form_alter of your form, and add your own validation to it.

function YOURMODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if($form_id == 'NAME_OF_FORM') {
    $form['#validate'][] = 'YOURMODULE_VALIDATE_FUNCTION';
  }
}

function YOURMODULE_VALIDATE_FUNCTION( $form, &amp;$form_state ) {
  $mobile = $form_state['input']['field_MOBILE']['und'][0]['value'];
  $is_valid_mobile = YOUR_AWESOME_MOBILE_VALIDATOR($mobile);
  if( !$is_valid_mobile ) {
    $error_msg = 'Mobile is invalid. Please enter a valid mobile number e.g xxx-yyy.';
    form_set_error('field_MOBILE', t($error_msg));
    return false;
  }
}