sentences:  While there are several different varieties of virtual queuing systems, a standard First In, First Out that maintains the customer's place in line is set to monitor queue conditions until the Estimated Wait Time (EWT) exceeds a predetermined threshold.When the threshold is exceeded, the system intercepts incoming calls before they enter the queue.It informs customers of their EWT and offers the option of receiving a callback in the same amount of time as if they waited on hold.