Upgrade to PHP 5.4 results in PHP error in drupalroot/include/theme.inc - line 1074

I'm posting as documentation and have already set the status to fixed.
I upgraded to Ubuntu 12.10 which include PHP 5.4. My fix was to downgrade back to PHP 5.3.

cck_phone I'm using is 7.x-1.x-dev - 2012-Mar-02. My drupal installation is 7.16.

After upgrading to PHP 5.4 I started getting the WSOD. /var/log/apache2/error.log had the following error:
PHP Fatal error: Unsupported operand types in $drupalroot/includes/theme.inc on line 1074, referer: http://cows/views/people/employees

I tracked it down to the following lines in cck_phone.module: line 287 and 318.

// Extension
if (!empty($element['extension'])) {
  $phone = $phone . theme('phone_number_extension', $element['extension']);
}

Variable $element['extension'] is a simple string. The theme.inc theme() function expects an array. $element['extension'] becomes '$variables' in the theme function. The error occurs on line 1074 when the $variables array is appended to.

// Merge in argument defaults.
  if (!empty($info['variables'])) {
    $variables += $info['variables'];
  }
  elseif (!empty($info['render element'])) {
    $variables += array($info['render element'] => array());   // line 1074
  }

I'm just learning PHP and don't know what the real fix is, but I'll stick to PHP 5.3 in the meantime