NB9/NB9W - Can I use a duet phone line?

When connecting a normal phone line into the "Line" port on the back of the NB9 / NB9W, you will be able to receive incoming PSTN calls, and also make outgoing PSTN calls. However, when connecting a Duet Phone line into the "Line" port, you may not be able to receive the different ringtones to signify an incoming call on one of your your two phone numbers.

The handset/s connected to the NB9 / NB9W will still ring upon an incoming call, and will still be able to make an outgoing call, however, you will not receive the different ringtones for the different phone numbers.

Unfortunately, this seems to be a hardware limitation of the NB9 / NB9W, and it is uncertain if this is able to be changed.