| Number | Name | Date | Kind |
|---|---|---|---|
| 4677657 | Nagata et al. | Jun 1987 | |
| 4759056 | Akiyama | Jul 1988 | |
| 4897866 | Majmudar et al. | Jan 1990 | |
| 4928306 | Biswas et al. | May 1990 |
| Entry |
|---|
| Matuo et al., "Personal Telephone Services Using IC-cards" Jul. 1989, IEEE Communications Magazine pp. 41-48. |
| Perry, Tekla, "ISDN devices unveiled," Jun. 1989, The Institute (IEEE) p. 9. |