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To answer your question on the Substitution Template first, the Sub Template CAN be used to send 10 digits to the end equipment if another quantity of digits is received. The Sub Template works on the egress, so you use it on the interface the call is leaving the ATLAS.
From what you wrote, I believe you need to look under the DIAL PLAN in the GLOBAL PARAM and make sure the "Area or City Code" is blank. If the area code is in there, the ATLAS will usually strip off the area code and only pass the 7-digit number.
You can verify the digits the ATLAS is receiving on the inbound call by going to SYSTEM CONFIG and then to EVENT LOGGING and setting "ISDN Events" to INFO. You can then view the events under SYSTEM STATUS in the EVENT LOG. You should see something line "Call to ATLAS 2565551212" where "2565551212" is the phone number received. (Remember that if the area code of 256 is listed in the "Area or City Code" then the ATLAS will still recieve "2565551212" but will then strip off the area code before processing the call through the Switchboard.)
Hope this helps,
Thanks Patrick! All seems to be working now.