Crud. I just wrote a few pleasant sentences of a nice solution to your problem (which I just assumed would be "install MacPorts, open a terminal and type 'sudo port install asterisk'"). Then I discovered that neither macports nor fink has asterisk. D'oh!
Actually, I'll paste my wasted time because if you don't know about using a package manager, you should. (AND you can read this while I try to actually help you with your problem!) A package manager is the thing Linux fans are talking about when they say "our 'add/remove programs' can actually add programs, because they're all Free! Installing all the software you want is a really curious experience the first time -- at first, it seems too good to be true, and you almost expect to receive a large bill in the mail. Then you go through these giant lists and hierarchies thinking "hmm, I could use that; at least it's worth a try." Then you brace for bad news and hit "Apply" and, a little while later, everything is cleanly installed, with menu entries, init scripts, a layout on the file system that is actually consistent with the rest of your OS, etc. Later on, when the software is updated, it's a piece of cake because the software does it for you (sudo port update asterisk).
There are two such projects for OS X: Fink and MacPorts (recently known as "DarwinPorts"). Both are community projects, so in the beginning, it was Just A Guy who wanted his expensive Mac to have all of Linux's features and then some, so he started "porting" (making subtle tweaks to a program's code and installation process to make it smooth for others) free/open source Linux and unix software to OS X. Add some people and momentum, and while the Mac package managers will never be as complete as the *nix ones, they're still indispensable.
Personally, I use MacPorts because it tends to have what I need. Don't install both of them (waste of disk space, leads to collisions, just generally confusing and goffy); just look at the lists on their websites to figure out which fits you best.
brb with real help, i think i've guessed your problem
- First, make sure you have the Developer Tools installed. They're on your OS X disc or were included with your mac.
- Try what you were doing before, because that might have been the whole problem.
- Download a fresh copy of Asterisk, and move that file onto your desktop. Double-click it and OS X will untar it for you.
- Open Terminal. type
cd
Make sure you leave a space after "cd "
- Drag the folder you previously untar'd onto the terminal. This just types in the whole path to the file for you -- easy and typo-free. Hit return.
- (whoa, asterisk is missing a lot of instructions) Type
./configure
and hit return.
- Then you can
sudo make install
Enter your password.
That's a solid start, at least.
The only other thing that could go wrong is if you don't have some of those libraries that are required:
- dfs
- ncurses, and associated -devel
- openssl, and associated -devel
- zlib, and associated -devel
bison, and associated -devel (1.0.X only)
You can use your new port skills if you do to install any of those, ie:
port search ncurses
sudo port install ncurses
etc. It's good to search first so you can get the spelling of the name right.
Finally, two points:
1. Ask for help before you waste 48 hours on something like this!

2. Include some information about what errors you're getting so people can actually help you. I'm driving completely blind here!