A method comprising: receiving, at a machine type communication-interworking function, MTC-IWF, capable of operating in compliance with one or more 3GPP LTE standards including LTE-Advanced, a Device-Action-Request, DAR, command from a service capability server , SCS, through a Tsp interface , the DAR command including a Device-Action attribute value pair, AVP , having an user equipment identifier (231A/B, 241A/B) to indicate an user equipment to receive a trigger message initiated by the SCS , an SCS-Identifier for the SCS , an Action-Type AVP set to a value of 4 to indicate a device trigger replace request to replace the first trigger message with a second trigger message, a Reference-Number AVP set to identify the second trigger message and an Old-Reference-Number AVP set to identify the first trigger message; forwarding the device trigger replace request to a short message service-service center, SMS-SC ; determining a status of the device trigger replace request responsive to an indication from the SMS-SC of a success or failure to replace the first trigger message with the second trigger message; and sending a Device-Action-Answer, DAA, command to the SCS through the Tsp interface , the DAA command including a Device-Notification AVP having the UE identifier (231A/B, 241A/B), the SCS-Identifier , the Reference-Number AVP , the Action-Type AVP and a Request-Status AVP set to a value to indicate success or failure of the device trigger recall request; wherein the value of the Request-Status AVP of the DAA command is set to 0 to indicate success, 110 to indicate trigger replace failure, and 112 to indicate original trigger message already sent, and the method comprises in response to the value to indicate success or failure of the device trigger replace request is set to 0, releasing a given identifier used to identify the first trigger message based on the value set to 0. receiving, at a machine type communication-interworking function, MTC-IWF, capable of operating in compliance with one or more 3GPP LTE standards including LTE-Advanced, a Device-Action-Request, DAR, command from a service capability server , SCS, through a Tsp interface , the DAR command including a Device-Action attribute value pair, AVP , having an user equipment identifier (231A/B, 241A/B) to indicate an user equipment to receive a trigger message initiated by the SCS , an SCS-Identifier for the SCS , an Action-Type AVP set to a value of 4 to indicate a device trigger replace request to replace the first trigger message with a second trigger message, a Reference-Number AVP set to identify the second trigger message and an Old-Reference-Number AVP set to identify the first trigger message; forwarding the device trigger replace request to a short message service-service center, SMS-SC ; determining a status of the device trigger replace request responsive to an indication from the SMS-SC of a success or failure to replace the first trigger message with the second trigger message; and sending a Device-Action-Answer, DAA, command to the SCS through the Tsp interface , the DAA command including a Device-Notification AVP having the UE identifier (231A/B, 241A/B), the SCS-Identifier , the Reference-Number AVP , the Action-Type AVP and a Request-Status AVP set to a value to indicate success or failure of the device trigger recall request; wherein the value of the Request-Status AVP of the DAA command is set to 0 to indicate success, 110 to indicate trigger replace failure, and 112 to indicate original trigger message already sent, and the method comprises in response to the value to indicate success or failure of the device trigger replace request is set to 0, releasing a given identifier used to identify the first trigger message based on the value set to 0. <EOS>