Currently you cannot share your contact lists in SmarterMail. The 2 contact lists available to a user on WebMail or via Syncing, My Contacts and Global Address List. Changes to our backend and sharing code allow us to add this functionality in the future.
One alternative is to create a single user dedicated to storing these contacts and syncing that account on CalDAV sync for each of the desired users who wish to have this list. This isn't really elegant at all though, and I believe contact sharing is on our Feature "To-Do" list.