The blog post tells us a release has occurred, who wrote it, who the FSF is, what the relationship between Witch and Free Call is. However I can't for the life of me figure out what GNU SIP Witch is.
Here: http://www.gnutelephony.org/index.php/GNU_SIP_Witch I found this by following two links from the article. But it was random luck, I agree with you that the article lack of some important informations.