Although there were many hardware/design similarities between the Norstar systems and larger Meridian 1/Meridian SL-100 systems, the telephones themselves could not be used interchangeably between the key system and PBX. They were, however, backward compatible on their respective switch. That is, the oldest Meridian M7000 telephones can be used on the newest Business Communication Manager system. The latest T7000 series telephones can also be used on an older Norstar system such as the DR5.1. This allows companies to invest in hardware as needed.