Hi!
I have written a small php script, which sends SIP requests and displays the responses. http://obelix.ict.tuwien.ac.at/sip-gen/sip-request-gen.php
It's far away from finished (->todo.txt). Feel free to use it or download the source http://obelix.ict.tuwien.ac.at/sip-gen/sip-gen.zip and add new functionality or bug fixes :-)
Regards, Klaus