I used Google Voice since when it was GrandCentral but I finally decided to port my number out. The port completed yesterday and the service is working well so far. I have calls forwarding to both my cell phone and a SIP account, with voicemails going to my email.

I found these links useful:

• https://fabriceleven.com/travel/how-to-port-google-voice-to-voip-ms-for-project-fi/
• https://wiki.voip.ms/article/Porting_a_Number
• https://wiki.voip.ms/article/FAQ