General idea about the Source code structure you can get browsing the SVN repository

Switchfin relies on external and local packages. The external packages like Asterisk for example are obtained directly from their
original locations and are customized/patched by the Switchfin building process
The local packages however are stored in the root folder of the Switchfin SVN repository. Currently we have:

https://switchfin.svn.sourceforge.net/svnroot/switchfin/asterisk-gui
https://switchfin.svn.sourceforge.net/svnroot/switchfin/lec
https://switchfin.svn.sourceforge.net/svnroot/switchfin/mISDN
https://switchfin.svn.sourceforge.net/svnroot/switchfin/mISDNuser

Switchfin building process uses those local packages and you should not worry about them. 

The main Switchfin code is located in the SVN root under the name switchfin and this is what you need to download on your computer.

https://switchfin.svn.sourceforge.net/svnroot/switchfin/switchfin

As many projects under version control we have 3 subfolders inside switchfin, trunk, tags, branches.

trunk is the where the most recent code is kept. If you want to test the latest Switchfin features you need to check out the trunk folder

svn co https://switchfin.svn.sourceforge.net/svnroot/switchfin/switchfin/trunk   switchfin

tags is the place we put the stable releases. If you want to compile code for a production box please use the suitable release from the tags folder 

svn co https://switchfin.svn.sourceforge.net/svnroot/switchfin/switchfin/tags/br4-ui2.15 switchfin-br4-ui2.15                   

branches is the place we test some ideas which we are not sure will go in the trunk mainstream. If successful the code from the branch will be merged in the trunk.
You should not worry about branches unless you are Switchfin developer.