Main Page | See live article | Alphabetical index Grandfathered systems: Systems, including but not limited to, (a) PBX and key telephone systems, directly connected to the public switched telephone network on June 1, 1978, that may remain permanently connected thereto without registration unless subsequently modified, and (b) systems that are of the same type as those connected to the public switched telephone network on July 1, 1978, that were added before January 1, 1980, and that may remain permanently connected thereto without registration unless subsequently modified. Source: from Federal Standard 1037C This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.