Thank you c3c3 and AnveoRep! I checked On "Do not answer the line" in the Start of the Anveo Call Flow, and it worked along with a simple call flow (suggested by AnveoRep) that doesn't pick up the line to detect Fax, etc. Thinking about this further, I don't want any item in the Call Flow to answer the line for at least 30 seconds, so Google Voice rings my other phones and eventually directs to Google Voicemail. So, when Google Voice forwards to my Anveo DID, these are the settings in the simple Anveo Call Flow that works for me:
C) START (Do not answer the line) -> SIP Legacy (ATA device, 45 seconds) -> VOICEMAIL.
Google Voicemail picks up in 30 seconds, so Anveo's VOICEMAIL should never pick up. However, when someone calls my Anveo DID phone number directly, then Anveo's VOICEMAIL will pick up if I don't answer my SIP OBi202 phone.
Anveo Call Flow is indeed very powerful (better than Google Voice, for calls), and I ported my landline number to it last year. However, I don't port my Google Voice number because Anveo doesn't have free SMS or smartphone app, like Google Voice does.
Interestingly to continue on, would it be possible to restore Anveo's Call Flow GOODIES to detect an incoming Fax (at least when calling my Anveo DID without Google Voice)?
D) START (Do not answer the line) -> SIP Legacy (ATA device, 45 seconds) -> GOODIES -> FAX or VOICEMAIL.
If someone calls my Google Voice which forwards to my Anveo DID number and this Call Flow, then GOODIES will never be reached, since Google Voicemail picks up after 30 seconds. This is OK. For faxes, I tell people to call my Anveo DID number directly, then rings my SIP OBi202 for 45 seconds, and goes on to detect the fax.
The problem I see is that I could pick it up the ringing SIP OBi202 phone, hear the fax tones, and then disrupt GOODIES' fax detection/reception. If I pick up the SIP OBi202 phone and it's a fax, is it possible to press a key sequence that will transfer the call back to GOODIES/FAX? How?
E) START (Do not answer the line) -> IF (dialed number = Anveo DID) -> GOODIES (OK to answer the line since it's not coming from Google Voice) -> FAX or SIP -> VOICEMAIL;
ELSE (dialed number not equal to Anveo DID, e.g. from Google Voice) -> SIP Legacy (ATA device, 45 seconds; never answer the line since it's coming from Google Voice) -> VOICEMAIL (fallback in case Google Voicemail didn't pick up).
I tried using the "IF" item (which shouldn't answer the line itself) in the Call Flow, but I couldn't get it to work properly. I used Call Variables such as RDNIS (not sure if Google Voice forwards RDNIS?), ANVEOPHONENUMBER and ANVEO.DIALED.NUMBER, compared as Text or Number with my Anveo DID with or without the "1" country code.
Thank you in advance to those Anveo expert users!