Skype does not use SIP.
A test number that
echos back anything you say could be a way to test.
sip:echo@iptel.org
I have outbound routing 456 set to "ring" it.
It does not actually ring but works right away after I dial
456#
There may not be many, especially since FreeWorldDialup lost its free aspect. There are other VoIP companies that permit SIP calling. None that I currently use.
Too bad VOIPo does not have test numbers ...
Suggestions:
Bookmarks