Yes, the ATLAS 800 does not allow you to "blank out" the area code. It must have a 3 digit number there of some type.
I worked with you on your Support ticket for this, and what I did was under the DIAL PLAN, and GLOBAL PARAMETER, I went into the NUMBER TYPE TEMPLATE and changed the 10-digit pattern from being a TYPE of NATIONAL to UNKNOWN. (You already had the area code set to your local area code, which we left.) The NUMBER TYPE change appears to have cleared the issue of the ATLAS adding the area code to the CALLING PARTY #, which was making it a 13 digit number rather than the 10 digit number it should have been.
Nice working with you,