Abstract: Coupling device for the connection of a Data Circuit Terminating Equipment DCE to a given Public Switched Telephone Network PSTN and to a local telephone set. The coupler includes means for providing said local telephone set with DC current whereby the microphone and the headphone of the telephone can be used respectively for transmitting and receiving vocal messages from the a DTE which is connected to said DCE. The invention also provides a DCE for the connection of a DTE to a a PSTN and to a local telephone set including a coupler circuit having the electronic components matching the electric requirements of a given PSTN. The coupler further includes means for providing the telephone set with DC current whereby vocal messages can be transmitted and received from the DTE to the telephone set.