I transferred my old home phone number to google voice and now receive my home phone calls from google voice over a small Obihai box (one time cost $40) connected to my router and my home phone. It works seamlessly over my home phone and I receive home phone service for free (incoming and outgoing going through google voice.) Google voice only ports numbers from cellphones, so I first ported my number to a tmobile prepaid (cost $6 for a Sim card) and then ported to google voice. The whole setup took me 15 minutes. (Other than buying the Obihai 100 and porting the phone number. The porting took a day.) I also added 911 service for $1.50 a month through Callcentric since google doesn’t support 911. This is optional. And, yes, you can take your phone number with you to anywhere in the world, temporarily or permanently.
I also ported my cell phone number to google voice and now use it over my cell phones data plan (unlimited) so I never use voice minutes. I use tmobiles $30 month unlimited data with 100 voice minutes. (I don’t need the voice minutes since all my voice calls are using data through google voice.) You need an android app called GrooVeIp for this. (Free)