A method and system for populating identities in a message service involves registering a user of a first messaging service with a second messaging service. User identities for users other than the registered user may be identified. These user identities may be associated with the first messaging service and may be stored in a list associated with the registered user. It is determined if each identified user identity has a matching user identity associated with the second messaging service. If so, a database associated with the second messaging service is populated with the matching user identities. Determining whether a matching user identity exists may be performed, for example, by making character strings comparisons between user identities or using a database that stores a mapping of first messaging service user identities to second messaging service user identities. The mapping database may be generated as corresponding user identities are discovered.