I just switched from GV to Anveo, and it went pretty well. I already had an Anveo acct for E911. On my first attempt, after deleting GV from SP1, I went to the Approved Provider page and clicked Anveo, then selected my Obi and SP1, then since I already had E911 I selected "Reprovision existing account". WRONG! You must pick "Create account" -- it will give you the opportunity to log into your existing account later. Yes, it IS confusing.
After completing setup at Anveo, you have to go back to the Obi Dashboard and configure the Anveo SP1 service to be the default for outgoing calls AND E911. Your old E911 on SP2 should be deleted.
I did not port my GV#. GV seems to forward to my new Anveo DID just fine. You should edit the call flow at Anveo to increase the voicemail answer time to 45 sec, so GV voicemail will get unanswered calls instead of Anveo.