Several years ago I bought an Obihai brand VoIP (Voice over Internet Protocol) adapters and obtained a free Google Voice number. I was able, after configuring the device, to simply plug in any POTS phone and be done with it. Unfortunately HP/Poly, which now owns the intellectual property of the former company Obihai, discontinued production, sale and support of all VoIP devices that work(ed) with Google Voice. My understanding is there are no currently-produced VoIP products from any manufacturer that work with consumer Google Voice, and there are no plans to add any.
To answer your specific question is you might need to talk to your ISP and ask. Perhaps you can, depending on the equipment they use, plug your existing phones into it and be on your merry way.
Of course, depending on your “phone company” you may currently be using fiber and/or digital signals once it leaves your house anyway.
OK, I didn’t answer your specific question so should probably stop rambling.