Did it. Look for calendar as it says when you are adding the button, and after or before you add the shop code, add this too.
// Go to PM center... [pm]
if ($context['user']['is_logged'] && $context['allow_pm'])
echo '
<a href="', $scripturl, '?action=pm">' , $txt['pm_short'] , ' ', $context['user']['unread_messages'] > 0 ? '[<strong>'. $context['user']['unread_messages'] . '</strong>]' : '' , '</a>', $context['menu_separator'];
And excuse me for no indentation. I don't deal with code like that.
Daniel if I were you I'd add this to the page sense the messaging is essential for people to know how they are paid and whatever.