The present invention relates to communications methods, apparatus and systems for correlating registrations with subsequent requests for service, e.g., calling or other services or active calls. In one embodiment requests and corresponding registrations are determined through a method of operating a session border controller (SBC) which includes the assignment of a registration instance identifier by the SBC to each registration request, sending a first message including the registration instance identifier to each user device in response to each registration request, and determining if subsequent requests correspond to the registration instance based on the registration instance identifier being included in subsequent requests. In another embodiment, after a SBC switchover, the new SBC forks a mid-dialog request received for a first call to all active registered devices having the same address of record and determines based on the responses which device has an active dialog corresponding to the first call.