To create debian source package you need some other projects sources that
jitsi depends on. In the same folder where jitsi is checked out do:
git clone https://github.com/jitsi/otr4j.git
git clone https://github.com/jitsi/libsrc.git
svn checkout http://irc-api.googlecode.com/svn/trunk/ irc-api
And then in jitsi do: ant deb-src -Dlabel=4444
This will create orig.tar.gz debian sources that can be used to debuild
debian package.