Number | Name | Date | Kind |
---|---|---|---|
2580439 | Kock | Jan 1952 | |
3189690 | Millett | Jun 1965 | |
3189691 | Simpson | Jun 1965 | |
3887771 | Spanel | Jun 1975 |
Number | Date | Country |
---|---|---|
2,260,401 | Jun 1974 | DEX |
Entry |
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"The 4A Speakerphone-A Hands-Down Winner," G. Reichard et al., Bell Lab. Record (USA), vol. 51, No. 8, Sep. 1973, pp. 233-237. |