A method for signaling an Integrated Messaging System (IMS) on an Internet Protocol (IP) based network to deposit a message, including the steps of sending a Session Initiation Protocol (SIP) SIP INVITE request to the IMS indicating a message deposit action; receiving a corresponding SIP message from the IMS agreeing to participate in the message deposit action; and sending an SIP acknowledge message to the IMS confirming receipt of the corresponding SIP message; and depositing the message in a destination mailbox. A method of signaling an IMS on an IP based network to retrieve a deposited message, the method including the steps of sending a SIP INVITE request to the IMS indicating a message retrieval action; receiving a corresponding SIP message from the IMS agreeing to participate in the message retrieval action; sending an SIP acknowledge message to the IMS confirming receipt of the corresponding SIP message; and retrieving the deposited message from a mailbox corresponding to known account information.