A method of operating a hearing system for conducting telephone calls as well as a hearing system capable of performing the proposed method. The hearing system includes a communication device (4) with a communication device microphone (3′) for picking up a first sound signal and providing a primary sidetone signal. The hearing system further includes a hearing device with a hearing device microphone for picking up a second sound signal and providing a secondary sidetone signal. A first amplification is applied to the primary sidetone signal and a second amplification is applied to the secondary sidetone signal. Adjusting of the first amplification is dependent on adjusting of the second amplification, or alternatively, adjusting of the second amplification is dependent on adjusting of the first amplification. The primary and secondary sidetone signals are then combined and subsequently output by a hearing device loudspeaker.