A headset system (1) comprising a first telecommunication device (3) comprising a desk phone or a computer (4) with an installed softphone, a second telecommunication device, such as a mobile phone or a smart phone (6), and a headset (2) comprising a cord (5) with a first connector (7), by means of which the headset (2) is adapted to be interchangeably connected to the first telecommunication device (3) and the second telecommunication device (6). The headset system (1) is adapted to transfer a call from the first telecommunication device (3) to the second telecommunication device (6), when the first connector (7) is unplugged from the first telecommunication device (3). The invention also relates to An external device (8) comprising a second connector (31) to be attached to a first connector (7) of a headset (2), means (9, 10) for connecting the external device (8) to a personal computer (4) with a softphone installed on it, a controller (36) adapted to send a call transfer control signal to the softphone, when the first connector (7) is unplugged from the second connector (31), whereby an active call on the first telecommunication device (4) is transferred to a second telecommunication device (6).