Changing the customers name in emails

Hi,
I have a site where there is no registration at checkout.

This has resulted in the emails for 'order creation notification' and 'order status notification' having 'Hi ,' at the start of the email.

To have the email start with 'Hi [billing address->first name],' what do I need to change in the code:
echo JText::sprintf('HI_CUSTOMER',@$data->customer->name);?>
and
echo JText::sprintf('HI_CUSTOMER',@$customer->name);?>

Thanks,
Geoff

Thanks Jerome

Hi refreshing this thread:

I put the following line in the "Order creation notification" template
<?php echo JText::sprintf('HI_CUSTOMER',@$data->cart->billing_address->address__title." ".@$data->customer->name);?>

In the e-mail to the customer the output is ""Hello Mr. XXXYYY".
But my Page is in German and the Shop (Select in Registration and Output auf Title in the shipping Adress) is korrect in German (Herr, Frau).
What I have to do, to get in the email the German Traslation of what User see on Webpage in the Select (drop down) for the Titel (Mr, Ms)?

Thank you