The only guys I know that actually return phone calls immediately, or call when they say they're going to call, are gay guys and my grandfather, who has nothing else to do with his time.
I think it's fairly typical for a guy to say "I'll call you tomorrow" and call sometime the next weekend. It doesn't always necessarily mean anything.
But if you called once, left a message, then called a few hours later to check and see if he got your message, you want to avoid being... well, being scary.
Relax... the guy seems to like you, he talked to his (or your) friend about you, give him a window of time to do the "typical-guy-doesn't-call" thing, and take it easy.
If this happens all the time, talk to him about it, but it sounds like you guys are just starting to start up a relationship, so try not to make a huge deal out of it.