| Number | Name | Date | Kind |
|---|---|---|---|
| 4484029 | Kenney | Nov 1984 | |
| 5504812 | Vangarde | Apr 1996 | |
| 5694467 | Young, III | Dec 1997 |
| Entry |
|---|
| Patent Abstracts of Japan, vol. 017, No. 412 (P-1583), Jul. 30, 1993 & JP 05 079855 A (Hitachi Ltd; Others: 01), Mar. 30, 1993. |
| Hello Direct "Catalog of Telephone Productivity Tools" Spring 1994, pp. 6-7, published in USA. |