If you call the next day, you are being predictable, and look needy, and it works better if you make her think and wait at least one day, you should know this, it even in the movies!!!
This is one of the biggest myths out there. Like you said, it's in all the movies, everyone's seen Swingers, this is nothing new.
All of my male friends wait 2-3 days before calling.
All my female friends/former roomates KNOW that guys wait 2-3 days just to look cool, not because they're actually busy. Girls are not stuipid, they know which guys are stock brokers who spend 24 hrs on the phone, and which guys sit at home playing hard to get.
There is NOTHING unique about calling 2-3 days, it's a social norm nowdays, almost every guy does it. Don't kid yourself, it's very predictable.
If the girl thinks you're hot and you wait 2-3 days, they'll probably let it slide, but if they were only moderately interested, the waiting period will turn them off, and they'll flake on you. My wingwoman does it all the time.
I'm telling you from field experiance, the best way to prevent girls from flaking out on you is:
1.) Ask her out first before asking for her number. If you jump right to the number close, that's all you will get, a number.
2.) Call the next day.