non Gigaset PRO handsets will work behind the N870/N670. We have even seen that certain GAP handsets cause instability in the system and therefore limited the usage of GAP handsets.
Gigaset can not guarantee that
We allow to disable the GAP handset limitation via auto-provisioning, see below for more information.
When this option is disabled and instability is reported, Gigaset will not investigate these instability issues. The GAP limitation needs to be enabled again and if then still instability occurs, support is guaranteed.