you need register one of the sip service on your SPA1001, such as nonoh.net, the settings is here http://www.nonoh.net/en/sipp.html, ipkall cannot register on SPA1001, it only send call to your ATA. real on ipkall.com for forwarding.
read my blog for ipkall forwarding http://blog.wenxuecity.com/blogview.php?date=201008&postID=6250