What to do?

I'm in a pretty serious long distance relationship. We're doing pretty good, except when he's been calling lately. I've noticed we have a lot of blank, silent moments. I feel like we've talked about everything there is to say, but I can't stand not hearing his voice! Talking less isn't really an option, because we can't see each other for a while and it's too hard to keep the relationship going w/o communicato. What can we do to fill these blanks? Any ideas? Thanks so much!