Can you even attach a POTS or POTS like device to Google Voice anymore? I was looking into this last month and it seemed like they had removed that feature and the devices people were using (they had stopped selling them some years ago) to do it stopped working recently.

I have an Ooma phone now and I just plugged my existing phones into the Ooma box which then works the same as an old landline for the most part.

Just put a Google Voice line behind a FreePBX or Asterisk and you get all the call filtering you want. You can even make your internal numbers or whatever.

I first found the Tin Can cool, but now seeing their privacy policy, it's definitely nothing for me. I'd just use a normal VoIP cordless phone (e.g. Gigaset makes various models), or even a normal corded phone with a VoIP ATA. Some of them might even have integrated whitelisting, but I didn't check.