The Extended Phone Services (or device-specific phone services) include all extensions to TSPI defined by the service-provider. TSPI defines a mechanism that enables service-provider vendors to extend TSPI using device-specific extensions. TSPI only defines the extension mechanism, and by doing so provides access to device-specific extensions, whose behavior is completely defined by the service provider.
TSPI consists of scalar and bit flag data constant definitions, data structures, functions, and callback messages. Procedures are defined that enable a vendor to extend most of these, as described in the topics in this section.