Does anyone know what the field "ship_code_id" is used for? It is part of the jos_vm_products table.
Reviving this to provide an answer of sorts. The ship_code_id is apparently not used for anything, according to this post:
http://forum.virtuemart.net/index.php?topic=7354.0
But I think it could be used for creating a shipping module that would allow a greater degree of customization and even a per-item shipping cost. It's mentioned in task #31 in the Developer's Wiki but I don't see any other reports of anyone working on that option.
It would be lovely if someone were able to write a shipping module making use of it, but first the field would need to be accessible in the product form page and that would require some hacking of the core code. Not that that's a bad thing, necessarily...