A system and method for immediate and delayed real-time communication activities using availability data from and communications through an external instant messaging system, that operates to obtain aggregated user online presence information through its own client software, through interception of client-server communications between an external instant messaging client and server, and through other available interfaces to user account information on such external instant messaging systems. The system operates to gather user online presence information in part by intercepting communications between an instant messaging client and the Internet. The aggregate presence data, as well as other information describing the availability of a user, is used to intelligently route real-time communications, such as instant messages and phone calls. The disclosed system further implements a technique for waiting for changes in a user's availability status, and for performing actions on a user's behalf in response to such changes in availability status.