Expected Number of Digits
Enter the number of digits the table
expects to receive from the telco. Use this
program to make the system compatible
with 3- and 4-digit DID service.
If ISDN trunks, we analyze the last digits
that are set here. If it is T-1 or analog DID,
it analyzes the first digits that are assigned
here.

I am fairly certain that if you get AAA-BBB-CCCC that you can set it for 4 and you will analyze CCCC. Not certain. That is very un-standard to send 10 digits. Seven usually in large networked systems.