What Jain SIP (java) classes should be used to create a SIP client?

I ask you to create a SIP client, but I completely lost ... After some research, I found the Jain SIP API in java, and I think I will use it. However, I do not know which classes I should use and which interfaces I should implement or not.

I read this article: http://www.oracle.com/technetwork/articles/entarch/introduction-jain-sip-090386.html

And this: http://hudson.jboss.org/hudson/job/jain-sip/lastSuccessfulBuild/artifact/javadoc/javax/sip/package-summary.html#package_description

But I do not understand, what part should I implement for the SIP client? SipListener OR SipStack and SipProvider?

Thank.