In a call center environment, applications may need to accumulate data about a call (such as IVR input of account numbers) that is desirable to have available to all agents and applications that handle the call. The variably-sized field, bounded by the dwCallDataSize and dwCallDataOffset members in the LINECALLINFO structure, gives the telephony application a way to provide to the service provider data to be passed along with a transferred call and made visible to other applications that are monitoring the call (either on the same PC, or, through the server, on other PCs). The LINECALLINFOSTATE_CALLDATA message indicates whenever this field changes. The lineSetCallData function allows an application that owns the call to set this data; LINECALLFEATURE_SETCALLDATA indicates when changing the data is permitted. The dwMaxCallData member in LINEADDRESSCAPS indicates the maximum number of bytes permitted in this field. Initial call data to be attached to a call can be passed to the service provider in LINECALLPARAMS.