Developers may be invited to initially pursue less extensive interoperability testing than would be implemented through full Compatibility Testing. Registered Product testing is designed to recognize third-party products that have demonstrated an initial level of interoperability in the Nortel laboratory environment and are thus deemed registered with specified Nortel products. Third-party developers will receive an acknowledgement letter that a successful call completion was made with a Nortel product and will be encouraged to complete testing to achieve Nortel Compatible Product status.