How to use different short description in shop page and in product page in woocommerce

The short description template is /templates/single-product/short-description.php :

<?php
/**
 * Single product short description
 *
 * @author      WooThemes
 * @package     WooCommerce/Templates
 * @version     1.6.4
 */

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly

global $post;

if ( ! $post->post_excerpt ) return;
?>
<div itemprop="description">
    <?php echo apply_filters( 'woocommerce_short_description', $post->post_excerpt ) ?>
</div>

You can override this (or any woo template) : http://docs.woothemes.com/document/template-structure/ by copying the file into your theme… so woocommerce/single-product/short-description.php. Then you can edit it as you like.

EDIT: If I understand your question you would do this:

<?php
/**
 * Single product short description
 *
 * @author      WooThemes
 * @package     WooCommerce/Templates
 * @version     1.6.4
 */

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly

global $post;

?>
<div itemprop="description">
    Entre em contacto connosco para saber preços Aqui
</div>

Or you could filter woocommerce_short_description. Or you could define your own woocommerce_template_single_excerpt() function which is pluggable, or remove it entirely from its hook. There really are many ways to do this, but the template override tends to be the simplest to understand.

EDIT: Here’s a very basic example of how to filter the short description (and in general filtering anything is always the same process)

Edit again: this goes in your theme’s functions.php

function wpa_98244_filter_short_description( $desc ){
    global $product;

    if ( is_single( $product->id ) )
        $desc .= ' add some extra text to the short description';

    return $desc;
}
add_filter( 'woocommerce_short_description', 'wpa_98244_filter_short_description' );