He does it to me all the time. And yes I've voiced my upset to him. In subtle ways of course and he'll keep up the communication for a while. Then work takes over and it's like he forgets. I love him with all my heart and I know he loves me too. I just need a little attention sometimes you know?
I'm fond of plain words said neutrally. "I'd like to talk soon, could you reply ____ (today, tomorrow, within 3 days etc)." And if treating him like an adult doesn't work - stop talking. Say "hi" now and then to let him know you're still available but otherwise move on.