ETel telephony extension modules—TSYs—translate between client side API function calls and the instructions understood by a particular telephony device, or family of devices.
There is no requirement for a particular TSY to support the complete
set of functions defined in the client-side APIs, although typically a TSY will
support—as a minimum—all the functions in the core client side
API. ETel returns an error if a TSY does not include a called function—the error is TSY dependent, but should be
KErrNotSupported for any
TSY developed by Symbian.
This documentation does not provide information about the API used to create TSYs, as this is beyond the scope of most developer requirements.