I was sad the first day and never looked back!
My kids were already very independent before they graduated and gone a good deal of the time. We are very close, but generally spoke once a week, and IMd if we had more stuff going on. There were a few times DS #1 was home for the weekend and we never knew... He stayed at a friend's. I only knew by his cell phone bill. He was only an hour 20 minutes away, anyway. He came home on all of the usual holidays.
The other one called a lot his first year. Then he joined the military, but when he was not deployed we heard from him regularly. Now, he's back in school, but also married and working, so the communication is less.