PBXs with external ISDN connection
If you have a router that supports IP-telephony which also offers an internal ISDN-port (S0-port) you can generally connect the PBX's external ISDN-port to it. It is to note however that the PBX is now operated as a sub-PBX behind your router. Various features which are controlled by the network provider and operated by the PBX (such as call-forwarding via provider) can no longer be used. Since this is also dependent on the router we can't provide a listing of what exact features these are.
PBXs with external analog connection
If you have a router that supports IP-telephony which also offers internal analog ports you can generally connect the PBX's external analog port to it. It is to note however that the PBX is now operated as a sub-PBX behind your router. Various festure which are controlled by the network provider and operated by the PBX (such as call-forwarding via provider) can no longer be used. Since this is also dependent on the router we can't provide a listing of what exact features these are.
PBXs with external VoIP connection
If your network provider also provides you the necessary data (e.g. username, password) and allows operating alternate hardware, the VoIP-accounts can be configured directly in your PBX. A converter/gateway (e.g. VoIP-to-ISDN gateways) is not necessary. For this the PBX just has to be integrated in your network, so it can access the internet.