What has to be noticed in case of an incoming call?
An incoming call will also be signalized at the Bluetooth headset and can immediately be accepted by pressing the 'Accept button' (see manual of your Bluetooth headset producer).
If you accept the call with your Gigaset device, and afterwards want to transfer the call to your headset, you also just need to press the accept button at your headset. In this case, the transfer of the call could take between 3 and 5 seconds.
Within this period you should avoid to press the accept button twice, because you possibly could hang up the call.