Hi,
Well, you could either set a stock of 0 in these "call in" products, or set a sale start date in the future or a sale end date in the past.
That way, they would still appear on the listings on the frontend (unless you turn off the "out of stock" setting of your products listings menu items / modules for the stock), but they won't be purchasable.
And you can tweak the text displayed ( "out of stock", or "not yet on sale" or "not sold anymore" ) with a translation override:
www.hikashop.com/download/languages.html#modify