If you want to build OpenSIPS package for debian/ubuntu from svn, that this is post for you.
First, checkout OpenSIPS sourses from svn as described here.
For example, to download latest 1.6 branch do:
$ svn co https://opensips.svn.sourceforge.net/svnroot/opensips/branches/1.6 opensips
Enter opensips directory and move debian-directory on top-level:
$ cd opensips
$ ln -s packaging/debian debian
Increase the Debian release number:
$ debchange -i
Finally, build package:
$ debuild -us -uc
Debian packaging utilites can be installed with "sudo aptitude install devscripts build-essential fakeroot".