I have other people looking into this, but I thought I'd spell it out here in the hope that somebody has already invented this particular wheel. I'll listen to any offers (and detailed explanations of a better way to achieve this), but, in the absence of the Commercial Help forum (pleeeeease can we have that back dev team? - it only takes a minute to add a forum!) please send any commercial responses via PM or e-mail.
Purpose: To allow free (or paid for express) delivery to certain postcodes, whilst still allowing "normal" shipping options. Postcodes need to be set through Admin
Add an option in admin to enter and store a variable number of post codes (I have about 20 to begin with - I'd suggest a comma delimited list similar to entering prices per weight in the Table Shipping.)
The php code to check the current "ship to" post code against these free delivery post codes - the check would need to take place after a new shipping address was entered as well as on first display of Step 1 of the Checkout.
If one of the stored postcodes matches the ship to postcode then the shipping module can display.
I think to someone thoroughly familiar with Zencart and proficient in php/MySql, this would really be quite simple - IF my thinking is right, it's simply a case of adding a table to the database, passing the "free" postcodes to it and recovering those codes to check against. But I'm a long way from being proficient in php/MySql!
So, I'd be looking for the file(s) necessary to create the Admin side and the snippet of code to perform the check which I could add to whichever shipping module I wanted to apply this to. The ones I am using (it's a 1.3 cart) are freeoptions and storepickup (the former being used for free delivery, the latter being used for express delivery to the same areas)