Adding a telephone field in product contact

Hello
I need to add a telphone field foe the contact form inside products. I know its the contact product file inside Views, but what is exactly the code to enter to ask the user for his/her telephone number?
I know its something like this but I dont know what to enter in the ?? places. Can I just put "Telephone" in those places?
<tr>
<td class="key">
<label for="data[register][??]">
<?php echo JText::_( '??' ); ?>
</label>
</td>
<td>
<input type="text" name="data[register][??]" size="40" value="<?php echo $this->escape(@$this->element->??);?>" />
</td>
</tr>
<tr>

Hello,
No, thats not what I want actually, I want the "telefone" field to appear in the contact form that is created when someone wants to ask about a specific product that has no price for example.
Like here:
www.galeriadeartepedropena.com/tienda/pinturas/92-alexandra-ii
you can see a link that says "Consultar Precio Por email" when you click on it you go to this page
www.galeriadeartepedropena.com/tienda/product/contact/cid-92
here is wher I want to add a Telefone field. So I guess I have to add a custom field but of what type? I cant find the correct one??

Hi

As soheilom requested I would also like to have a entry for "Phone" on the contact form. I think it is very useful for my business. Have you any plans to include this?

Or do anybody have a workaround?

nicolas wrote: You would have to edit the file "contact" of the view "product" via the menu Display->Views in order to add your additional input field:
<input type="text" name="my_field"/>

With the latest version of HikaShop, the contact email is now editable via the menu System->Emails (Business edition) so that you could easily add the value entered by the user in your contact form's input field:
echo $_POST;

Thank you for your answer. I have the essential edition, does it mean that à cannot edit the email ?