Lots of letter. I wrote every day. some days I would write 2. It is very hard the first few weeks for him and you both. My son just graduated 02Dec2011. I sent him funny pictures i found on the internet., I even wrote him jokes that were also found on the internet. They love to hear about sports, but somehow someone in the Div was very up to date. Ask lots of question. I found the more I knew about what he was doing the better it made me feel. I followed the navy weeks very close so i could send him encouraging messages before they started. Have you joined the navy recruit facebook page? http://www.facebook.com/NavyRecruitTrainingCommand?ref=ts loads of info. once you find out what div he is in you should join the group of parents who also have recruits. They are very supportive. Staying busy is important. But i did find those times that I just had to go sit in his room. I did his laundry (even tho it was already clean). Helped me deal with his absence. Remember its a long journey but the outcome is one of the greatest.
As soon as you know your child's PIR date, form a group. My group of PIR moms was my lifeline. We laughed, cried, shared stories. We are still close almost a year later. We now have our own facebook group. I never thought that I could bond so strongly with a group of strangers, but they are the ones who know exactly what you are going through. Good Luck to you and your recruit.