Guys, don't do it. I mean, maybe for a day or so, just to let her know that you're not desperate (because no one wants to look desperate), but don't leave a girl hanging for four or five days. It's just not nice.
First, she'll wonder why you didn't call. Then, she's start thinking of excuses for you. Eventually, she'll get really annoyed with you and tell her friends things like "Well, if he didn't like me, he shouldn't say he was going to call." Finally, she will decide that you're not worth her time. She'll go out with someone else and have a great time and tell all her friends that you're a waste of time, and you may actually be a decent guy who just forgot to call.
Don't let it happen to you.