This plugin, designed specifically for Zen Carts 1.5.5 and later, provides the same functionality as its earlier version.
Your Zen Cart store sells only virtual products (whether they be services or downloadable items), so your store has no need to collect your customer's shipping information. You still need to collect the customers' billing-address, possibly for tax-determination.
This plugin modifies the display of the checkout process, recognizing that the checkout_shipping page will never be used; the result is that your checkout process is reduced to checkout-payment choice followed by checkout-confirmation. Invoices generated by your store's admin contain no references to shipping addresses and there's no "Packing Slip" link on your admin's Customers->Orders page, since there's nothing to pack!
Note: This plugin supports Zen Cart versions 1.5.5 and later; if your store is running Zen Cart 1.5.1 through 1.5.4, you'll need to use All Virtual Products (No Shipping) instead.