Pick out which DID number will be your remote access number. Renumber the default remote access number to that. Found under System Renumber/Single/Remote Access. The default 889 is shown, press Enter and put in the new number and Enter.
Now make a Barrier Code, found under LinesTrunks/Remote Access/Barrier Code/Code Info. There are 16 "slots" to put different barrier codes into, and each one can have a different restriction level. Pick a slot, and make up a code (default length is 7 digits)
Now that that "slot" and assign it to SPM, LinesTrunks/Remote Access/Barrier Code/SProgMaint.
Now you're set. Dial in on the DID number, it will answer on the 2nd ring. Get a stutter dial tone, enter the barrier code, get another stutter dial tone, dial *10 and get the internal modem.