Westend61/Getty ImagesThere’s a gadget doing well in Australian online stores at the moment that retrofits a smartphone into a landline. You plug a coiled, corded handset into the charging port, and the smartphone is suddenly attached to a clunky plastic receiver you hold to your ear, cord dangling, the way phones worked before they became small and mobile enough to fit in a pocket. It costs about A$20, and appears to be a retro novelty accessor…