LIB--don't expect a call back. Some will, many won't.
Those that do are probably take-charge types and don't care what it signifies. Others have high IL or can't restrain themselves (psychos or high IL.)
Those that don't---with or without high IL---do so because it sends too many signals too early, signals that they're not ready to give up for free just yet--such as they're interested, or that you are their ownly option at the moment or....
I have seen this with the women at work (especially young ones)--it is a time of high stress, high interest, tons of speculation and signal reading. They are are on high-alert not to show lack of cool or desperation, or to give up control, or show desperation, or being unfeminine, or of showing desperation, or being a loser. And they don't want to show desperation, too. They're very busy reading all clues they've picked up from you, comparing these notes with other girlfriends, and hyper aware what clues they send you.
Take it as a rule: they will likely not call back. Don't read anything into it.
Just go over some of the basic phone handling skills and proceed anyway. If you can't reach her after 3 or so attempts (that's my magical number) count her as impossible to date and move on. I know of the "hey, what do you have to lose? Call her some more anyway..." stuff--and if you're feeling it, go for it. But walking away from a few of these situations does wonders for your sense of self---as in, desperation goes away because it's telling yourself "that one missed out, so I'm off to better things---I can afford letting this HB and 10 others not happen--I continually develop other options." It jacks up your self-perception and sense of ease, and others pick up on it. Try it.
Anyway--just for review:
--Call 5 days (or whatever works for you) after getting the number.
--Don't leave messages.
--If you don't get her, wait a few days (she has caller ID and knows it's you) and try again. AFC's will leave messages "so she can get my number, know it was me, and call..." She knows it was you, doesn't need your number and is under hightened alert about showing any desperation to you (such as calling.) AFCs make excuses about why she's unavailable, too. Just don't get started down any of those lines--if you don't get her, hang up. Try again days later.
--Prepare what you're going to say before hand with options and escapes.
--Stand up and smile while talking, you'll be more bright and in-charge (posture determines your mood) and it will carry in your voice.
--Keep the call under 5 minutes: some pleasantries (don't hurry) set the date, go.
--If she can't make it, see if she counter-offers.
--Remember, you're busy and have a full schedule, so don't go out of your way to make the date happen, only if it fits in with your schedule. If you have no schedule, pretend that you do.