Thanks for that, worked a treat

.
The hardest part is knowing just where to put the code.
I have removed the "Buy Now" button on product lists where the price is ё0.00 and replaced it with CALL FOR PRICES instead.
I have also removed "Add to cart" button in the product details pages for zero priced items and used the same message.
In the /skin/custom_scheme/customer/main/product_details.tpl file:
(The added bits are in red text. The other is part of the standard file and should not be removed):
{if $product.appearance.buy_now_buttons_enabled}
{if $product.forsale ne "B"}
<ul class="simple-list">
<li>
<div class="buttons-row buttons-auto-separator">
{if $product.price gt 0}
{include file="customer/buttons/add_to_cart.tpl" type="input" additional_button_class="main-button"}
{else}
<font color="red" size="2"><b>CALL FOR PRICES</b></font><br><br>
{/if}
In the /skin/common_files/customer/buttons/buy_now.tpl file:
{if $product.price gt 0}
{include file="customer/buttons/button.tpl" button_title=$lng.lbl_buy_now additional_button_class=$additional_button_class|c at:' add-to-cart-button'}
{else}
<font color="red" size="2"><b>CALL FOR PRICES</b></font><br><br>
{/if} {* END TEST *}
I have included the above for anyone using V4.4.3 who may have the same enquiry. Ours is a customised site so the file shown above in the custom_scheme folder will probably be in the scheme folder for the site.
Hope this helps.
Denis.