third party manufactures another embodiment of the present invention is shown in fig2 in this exemplary embodiment the accessory device is represented by a head set 30 that can be used with the mobile phone 1 and allows a convenient conversation even in situations where it is not possible to hold the phone in the hand for example during driving in a car or in similar situations although it would be possible the connect such head sets via a cable 31 shown in dotted line to the mobile phone 1 a wireless connection is used in the situation shown in fig2 preferably the wireless connection is obtained by a communication link 35 in accordance with the known bluetooth u2122 standard the mobile phone 1 comprises therefore communications means 6 for establishing a bluetooth u2122 link 35 alternatively the communication link 35 could also be realized by a wlan link or another radio interface again the control unit 2 of the mobile phone 1 will check the origin of the head set 30 for this the head set 30 is adapted in such a way that it transmits an identification information via the communication link 35 to the mobile phone 1 which identification information is analyzed by the control unit 2 in case the control unit 2 recognizes the head set 30 as being a certified product the hands free option by using the head set 30 is enabled the user of the phone 1.