This read-create DisplayString holds the Service Profile Identifier (SPID) for the second channel of this Terminal Endpoint, a 9-20 digit numeric string required by some ISDN switch protocol types such as Bellcore NI-1 and NI-2, and is a zero-length string if not needed. An admin configures it alongside isdnEndpointSpid when the ISDN line's second B channel also needs its own SPID for the switch to register it. On a Basic Rate Interface where the provider requires per-channel SPIDs, leaving isdnEndpointSpid2 unset would keep the second channel from registering even if the first one works fine.