The present invention provides a method and system for assuring H.323 alias address portability to an H.323 user in real-time H.323 multimedia communications where the H.323 user is registered with a home gatekeeper for the home zone of the H.323 user. Alias address portability may be obtained using a central database that is known to the administrative zones and is used for alias address mapping, or alternatively, may be obtained by using a distributed database. The method may be implemented by: sending, by the H.323 user, a message with a called H.323 entity's alias address, to the home gatekeeper to originate a call to the called H.323 entity; confirming that the alias address, services, and service providers are portable; converting the alias address to a called routable alias address for the called H.323 entity and sending the alias address to the H.323 user; and placing the call to the called H.323 entity.