I had the same situation today.
My SIP UA was SIP enabled PBX (Avaya S8300 CM 2.0)
with SIP trunk. It was not configured to send
calling number. Once it was configured ("change
ISDN public-unknown"), the calls become possible.
So I thing your UA should try to send something
like calling number._______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
