The PHONEEXTENSIONID structure describes an extension identifier. Extension identifiers are used to identify service-provider specific extensions for phone device classes.
typedef struct phoneextensionid_tag {
DWORD dwExtensionID0;
DWORD dwExtensionID1;
DWORD dwExtensionID2;
DWORD dwExtensionID3;
} PHONEEXTENSIONID, FAR *LPPHONEEXTENSIONID;
Not extensible.
Extension identifiers are generated using an SDK-provided generation utility.
TSPI_phoneNegotiateTSPIVersion