Thank you for using the ADTRAN Support Community Forums.
In the ATLAS, the IN#ACCEPT (in the USER TERM) and OUT#ACCEPT (in the NETWORK TERM) determine how the call is routed. From what you described, I believe the IN#ACCEPT on your FXS ports are configured with "$". In the NETWORK TERM, the OUT#ACCEPT should be configured with "$" because dialing out, the number format can vary depending on local, long distance, or even international calls, but inbound calls should be a specific range of numbers.
The way to prevent outbound calls from ever routing back to another FXS port is to have the IN#ACCEPT be as specific as possible. It should be specific as possible because you do not want it to match a number that should go out to the PSTN. So if inbound calls are only presenting 4-digits, then the IN#ACCEPT can be "XXXX" and this will not match any outbound calls. But if inbound calls are 7-digits and you are in a 7-digit local dialing area (as opposed to a 10-digit dialing area), then you cannot use "NXX-XXXX" because this would match any local number you dial. If you can make it more specific it will not include local numbers destined for the PSTN. As an example, here at ADTRAN we could use an IN#ACCEPT of "963-XXXX" and be confident that range will not catch any number destined for the PSTN.
Hope this helps,