Hi Nick,
I have the PTR records published for my server's
public IP address. I
have the .sip_.udp.mobilia.it. 0 0 5060 sipserver.mobilia.it. record (I
tried it with and without the .mobilia.it added to the udp) published, I
tell the server to listen on the IP addresses which maps it's name in
DNS, I have a line after listen :
alias="mobilia.it" (I've tried both FQDN and this)
I have the feeling that your DNS records for your server are not o.k.
Show me your zone-files.
Cheers
Franz