AT&T MERLIN LEGEND Communications System PBX System Planning Manual page 157

Features
4-52 System Features
Because calls to the 15 area codes shown on Figure 4-4 should be placed on
the cross-country WATS trunks if all the northeastern WATS trunks are busy, the
number of the cross-country WATS pool, 890, is used in both cases. An FRL of 4
is assigned to restrict some users from using the cross-country WATS trunks.
Planning Form Instructions - Cotinued
7. Extra digits may be required for the system to place a call on a particular
pool. If so, enter the digits (0-9) in the same row as the pool number, in
the column headed "Other Digits."
These special accress or account codes can range from a single digit,
such as 9, to a maximum of 20 digits.
Extra Digit Example: If a business uses an alternate long-distance company for
calls to nine area codes in Canada, accessing the alternate long-distance
company lines requires getting a local line and dialing seven digits. The
completed form for the Area Code Table that routes these calls to the alternate
long-distance company lines is shown in Figure 4-5.