There is no auto-detect of SPIDs.
Basic-NI (National ISDN-1) REQUIRES SPIDs. That's the spec.
Basic-5ess and basic-dms MAY have SPIDs, depends on who configured the ISDN switch.
Other switch types don't use 'em.
Remember, SPIDs are pretty much a North American concept.

http://www.cisco.com/warp/public/129/bri_invalid_spid.html

"Currently, only the DMS-100 and NI-1 switch types require SPIDs. The AT&T 5ESS switch type may support a SPID, but you should contact your provider for information on what the SPID must be configured as. Remember that SPIDs are only required in North America and are configured only if required by your telco/provider."