The problem with this is, after 9/11 and the anthrax postal scares, programs where you could just sent stuff to anonymous, random GI's, whether christmas letters (e.g., Operation Dear Abby,etc.) or whatever, are no longer done for the safety of the troops. On one level this is a shame. I had great fun the last year I was in the service writing back and forth to a 2nd grade elementary school class while aboard ship. I found letters from many kids in the class in the box set out in the corridor for anyone who wanted such letters, so I wrote back to the whole class via the teacher.
Phone cards and phone calls are one thing that usually is reasonably affordable in the military. I know the Navy has a deal w/ AT&T for deeply discounted phone cards sold at exchanges and rates from overseas bases, for example.
Do you have a base near you? Most commands have an ombudsman (don't know what they call it in other branches besides Navy) who acts as a liason between the command and the families, especially during deployments. Such a person, or perhaps the Red Cross or a base public relations person might be able to tell you how to go about it.
breastfeeding, babywearing, homeschooling Heathen parent to my little Wanderer, 7 1/2 , and baby Elf-stone, 3/11!