A system and method are provided for communicating calendar appointment acknowledgements to a sender from a recipient device, in particular a mobile communication device capable of receiving SMS messages. The sender creates a calendar object comprising calendar event data, designates a recipient, and selects a transport method for delivering the calendar event data. If the transport method is SMS, then a calendar object message in plaintext SMS format is prepared, comprising a unique identifier, and transmitted to the recipient. The recipient's mobile communication device receives the SMS message and parses the message to extract the calendar event data, and transmits an acknowledgement to the sender including the unique identifier.