Messaging service interoperability methods. A client implements a messaging service version (X.Y), in which X is a major version number and Y is a minor version number. The client sends a PDU (Protocol Data Unit) with version (X.Y) to a server. If the PDU with version (X.Y) is not accepted by the server, the client reselects a messaging service version (Z.H), and sends a PDU with the reselected version (Z.H) to the server. Reselection of the messaging service version and sending of a PDU with the reselected version are repeated until the PDU is accepted by the server or all possible reselected versions have been selected.