Message-based notification that a called party is busy

One or more hardware-based non-transitory computer-readable memory devices storing computer-executable instructions which, upon execution by one or more processors disposed in a computing device deployed in an IMS (Internet Protocol Multimedia Subsystem) network configured for interoperations with an LTE (Long-Term Evolution) mobile network, cause the computing device to:

• receive a SIP (Session Initiation Protocol) INVITE message from a serving call session control function (S-CSCF) server in the IMS network indicating that a calling party utilizing user equipment (UE) is attempting a voice over LTE (VoLTE) call to a UE utilized by a called party;
• provide a SIP Busy message to the S-CSCF server in response to determining that the UE of the called party is busy;
• receive a SIP SUBSCRIBE message from the S-CSCF server indicating that the calling party has subscribed to a call completion service;
• supervise a busy state of the UE of the called party in response to the SIP SUBSCRIBE message;
• and
• generate an SMS (Short Message Service) message responsively to the supervision to notify the calling party that the called party is available to receive a VoLTE call.

A computing device configured as user equipment (UE) associated with a calling party, the UE arranged for accessing an LTE (Long-Term Evolution) mobile network, comprising:

• at least one processor;
• a user interface (UI);
• and
• at least one hardware-based non-transitory computer-readable storage device having computer-executable instructions stored thereon which, when executed by the at least one processor, cause the computing device to
• attempt to place a voice call over the LTE mobile network to a UE associated with a called party;
• receive an indication that the UE associated with the called party is busy on another voice call and that a message-based notification is available to notify the calling party when the called party is no longer busy and becomes available to receive a voice call;
• receive a message-based notification from a messaged-based notification service over the LTE mobile network that the called party is available to receive a voice call;
• and
• place a voice call to the called party responsively to the received message-based notification.