If you cannot anticipate the ip signalling originates from, you will need to use the external context. Allowing 0.0.0.0 is a terrible solution, since it allows anyone to assume the role of any extension on your pbx without authentication.
If you had the same trouble (487 response to an invite) then I would verify that you didn't mistakenly turn on auth-calls on the external context. If auth-calls is "false" you have a different issue, and need to address that directly.
If you had the same trouble (487 response to an invite) then I would verify that you didn't mistakenly turn on auth-calls on the external context. If auth-calls is "false" you have a different issue, and need to address that directly.