The call exists, but its state is currently unknown.

The call is being offered to the station, signaling the arrival of a new call.

The originator is dialing digits on the call.

The call has been established and the connection is made.

The call has been disconnected.

The call has been disconnected and is no longer active. This is the final state of the call before it's destroyed. A call can never transition out of the idle state.

The call was in the offering state and has been accepted by the called party.

The call is receiving a dial tone from the switch, which means that the switch is ready to receive a dialed number.

Dialing has completed and the call is proceeding through the switch or telephone network. This occurs after dialing is complete and before the call reaches the dialed party, as indicated by ringback, busy, or answer.

The station to be called has been reached, and the destination's switch is generating a ring tone back to the originator. A ringback means that the destination address is being alerted to the call.

The call is on hold by the switch. This frees the physical line, which allows another call to use the line.

The call is currently on hold while it is being added to a conference.

The call is currently on hold awaiting transfer to another number.

The call is a member of a conference call and is logically in the connected state.