A client-side signaling mechanism that allows a client to control how a telephone call is handled on a call server. The client user can create call routing rules on the client device using a client control component that manages session protocol messages. Once created, the call routing rule(s) created on the client are transmitted to the call server where a call routing component of the call server processes the rule(s) for a call related to the client. When the server receives the rule(s) and determines that the rule(s) are related to an existing call (incoming or currently in-process), the server halts current normal server rules processing for that call and executes the client-created rule(s). In one example, SIP session messages are employed for client control of server-side call forwarding.