I have noticed that when I use my Sipura ATA with Broadvoice, it uses
a special Broadvoice nameserver, so it's possible that that nameserver
resolves the name "BroadWorks". Is the realm supposed to be a DNS
name? I don't fully understand how the authentication works. Though
Asterisk does seem to work with Broadvoice, it does seem that
Broadvoice is pickier and more difficult to use than other services,
so I may decide to switch to a different one.