Actually it was very easy.
In administrator/components/com_virtuemart/html/
shop.cart.php find:
if (PSHOP_ALLOW_REVIEWS == '1' && @$_REQUEST['output'] != "pdf") {
// Average customer rating: xxxxx
// Total votes: x
$product_rating = ps_reviews::allvotes( $db_browse->f("product_id") );
}
else {
$product_rating = "";
}
(I had it already disabled)
And change with:
global $mainframe;
$comments = $mainframe->getCfg('absolute_path') . '/components/com_jcomments/jcomments.php';
if (file_exists($comments)) {
require_once($comments);
$count = JComments::getCommentsCount($db_browse->f('product_id'), 'com_virtuemart');
$product_rating = 'Number of Comments: '.$count. '<br /><a href="'.$url.'#comments">[Add Comment...]</a>';
}
else {
$product_rating = "";
}