There are three variants how the terminal connection is done, see http://www.hansenet-user-forum.de/viewtopic.php?t=16397 how to find our what one will get when ordering Alice DSL.
Now, when your variant is “NGN”, you get a “Sphairon Turbolink IAD”, which is a DSL modem with VoIP client, no (!) Router. You might combine that with a Fritz!Box (a model that can be used as Router only).
You may install the hardware at any time … it is not important to do this until 8:00 o’clock on the day when your connection is enabled, though Hansenet tells you so. But see this thread: http://www.hansenet-user-forum.de/viewtopic.php?p=185684. The only reason for early installation of the hardware is that a Hansenet technician in their service center may then start to configure your DSL profile.
If you have an ISDN backend, you must (!) use the S0 interface of the Sphairon IAD. So in order to use analog devices, you need a ISDN/analog converter or an ISDN phone box. See here: http://www.hansenet-user-forum.de/viewtopic.php?t=11230. A Fritz!Box may be uses as a ISDN phone box.