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H04M9/00—Arrangements for interconnection not involving centralised switching
H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
Procédé et dispositif pour rendre inintelligibles à un tiers assistant à une conversation par telephone, les paroles prononcées devant l'appareil téléphonique