http://www.avm.de/de/Produkte/FRITZBox/FRI..._7270/index.php
The new Registrar Feature for using Gatewayfunction is first implement on Fritz!Box 7270.
Later also on 7170 (the older/smaller one).
the right SW in early stage -but just working well on 7270- you can find it under the Fritz Lab on AVM HP.