He could be that busy, I know I tend to be and will sometimes forget to call even if resonably interested or not get a chance till to late. Especially if he doesn't own a cell phone, isn't at home, and/or shares a communal phone with several people.
Remember, we don't always start "to die for eager" when first liking someone. There are degrees of like.
Also, some people aren't good phone people at all, just like some people aren't email people. And many guys aren't very gregarious compared to women...
Now all this being said I'll share some simple rules I use to make relationships easier for me and allows me to retain more self-empowerment in them.
1. I view words such as "like" and "love" as verbs not nouns. So the person has to tyake actions towards me that indicate like or love not just express the sentiment: talk is cheap.
2. When I interpret this it lets me differentiate between what a person may feel, which I can't know not being a mind reader, and how we interact. This gives me two levels to judge both based on actions.
If the person is treating you with like or love everything is golden . . . if they are not then they either don't like or love you OR are unwilling or unable to express it in a way that YOU find meaningfull, which is just as bad.
An extreme example would be someone that loves you (feeling) but beats you (action). Unless your self-esteem demands beating this is not an acceptable expression of love to you and its time to bail.
The major advantage of thinking this way is that it decreases neurosis, you don't have to analyze what you think he/she might be feeling all the time. It gives an objective way to judge the quality of your relationship. And it puts the ball in your court because you are not sitting around letting someone else dictate the pace of the relationship based on you not wanting to screw things up with him/her, like starting to date others when you like that person but you aren't sure whether they like you.
OFcourse the flipside is you bare the responsibility of treating them with like or love . . . often times first.
Sorry for the long preface . . .
In your situation its less important what he feels and more important the way he is expressing it. Plus he's driving you a little nuts which is bad. In that situation I would definitely be looking around at others because he is either unwilling or unable to relate to you in a way that you want, even after you have spoken to him.
However, if you "Feel" really strongly, which can be hard to turn off, then I would treat him the way you want to be treated.
Don't just call him to chat, call him and ask him out on dates (which is what you want him to do). If he rejects you . . . well then you definitely know right?
This is just a personal insight but sometimes I can funk out a bit and not call because I am either going through a bit of shyness (contrary to popular opinion about my character) or a period of time where I am feeling bad about myself and unworthy of attention (guys can go through this too ladies!). A little encouragement when I am in that kind of mood can make all the difference.
I would be tickled if a girl a I liked asked me out and even if an attractive girl that I hadn't developed a lot of affection for asked me out on a date I would give her the benefit of the doubt and go.
Sorry for the long post I just wanted to share something that works for me. . . good luck and I hope things work out for you and you get want you want.
James
Feel free to email me if you want some more candid insights into the male psyche . . .

I think you ladies mess yourselves up because you give us more credit than we deserve and think we are more complex than we turn out to be.