It's scary to be alone. Loneliness is responsible for a lot of our impulsive decisions. The best thing to do is slow down before you call him for the third time, when he hasn't returned either of the first two calls. Slow down before you email him a nasty note about how disrespectful he has been by not getting back to you. You don't have to teach him a lesson or force him to "get it."
If he is not willing to put energy into you, you do not have to put energy into him. The next time that it's two in the morning and you're alone and missing just having someone, try to remember that desperation borne out of loneliness is not a beneficial reason to make a decision about your dating relationships.
So if you are anxiously awaiting a call that still hasn't come, go out and do something. Live your life. Get together with a girlfriend, go for a walk, exercise, read a book, whatever it is that you do to distract yourself and that you enjoy. It's not a replacement for having a partner in your life, but it does help to temporarily put the painful feelings aside so that you can more positive choices for your life.