Tips for staying in touch with him over the summer?

So I've been dating this guy for over a month (we met in my college Calc cl during the first semester and recently started dating). We aren't officially in a relationship yet, but we both really like each other and I really hope that we become a couple next semester. Summer break just started and he left this morning and I really really miss him... he lives several states away from me so I most likely won't get to see him over break since he will be doing a lot of travelling this summer. We already promised each other that we would send postcards to each other from wherever we go this summer, but do you have any other tips for staying in touch? We became really close and I really don't want us to lose that over break. He's a really amazing guy and I am so lucky that he likes me! Any suggestions?