[asterisk-users] Forcing SIP trunk matching order?

[James Lamanna]

Hi,
I have a bunch of different customers on an Asterisk Box (the PBX).
This Asterisk Box is behind another Asterisk box that provides a PSTN
connection.
Up to this point I've been using IAX between the 2 Asterisk boxes, but
I would like to use SIP instead.
After doing some testing I have the following issue.

If customer A calls customer B, but the call goes out through the PSTN
and comes back in, the call is rejected at the PBX because it wants
authentication.
I can guess that this must be because it matches the "To" address to
the friend SIP trunk that provides registration for the phone.
(All phones are setup as type=friend, host=dynamic). Is there any way
to force matching against the peer SIP trunk to PSTN so as to not
require authentication for calls
coming in from the PSTN server?

Thanks.

-- James