Specifies the level, linearity and frequency dependence of the magnetic field strength produced by the handset and characteristics for the calibrated probe coil in respect of all telephones having supra-aural earphones that can be connected to the Public Switched Telephone Network (PSTN) or Integrated Devices Digital Network (ISDN), which are intended for direct application to the ear and which provide, at the earphone, a magnetic field for coupling to hearing aids.