From the manual:
Receiving information from your service provider:
In return for providing the ordering information, your service provider gives you directory numbers and, if used in your area, Service Profile Identifiers (SPIDs). SPIDs are not provided for the AT&T 5ESS Custom service.
A directory number is the address or ISDN telephone number for the ISDN line assigned by the service provider. Each ISDN line receives at least one telephone number, called the Primary Directory Number.
If used in your area, your service provider provides you with the SPIDs. These are associated with the service you have ordered, and you must use these as part of the configuration for the Remote Office 9150 unit before any ISDN connections can be made (except for AT&T Custom). The SPID is similar to the ISDN telephone number and its format is unimportant as long as the information is entered correctly when configuring the Remote Office 9150 unit.