Postcards yes, calling no. What would an Illustrator have to say to an AD other then please hire me:)
Your art does the talking.
Also hearing AD's check out instagram, Pintrest, Behance.
I've seen attention given on Twitter as well, follow the AD's. They will occasionally tweet out an open call for subbing samples but just keeping abreast of what they are working on, who they like, what style they prefer (even who they are) all helps in your quest.