since this is thru Google, we know they store any and all data they have for future reference (this is in the fine print you agree to when signing up for any of their free services). While you can create an anonymous GV number with fake information, zip code, etc, eventually, you will want to forward all the hobby calls thru GV to your personal device.. ie. your cell or home phone. This creates a link between your personal cell/home number to the GV number, which I would think you would create/maintain your ATF SP's. Bear in mind pretty much anything you access and/or sign up for in the internet is traceable via your compute IP address.
Having said all the above, I don't mean to imply that GV is not a good alternative to a 2nd physical device, which is impractical for me at this time. I simply want to point out that if you have SO concerns.. you need to be a smart consumer/hobbyist and shore up any areas of exposure such as:
- Signing up for paperless statements with your device that you would fwd the GV to
- Don't share online access when it comes to your mobile phone web access since this have the date/time of your hobby calls via GV
- Make sure you place GV on Do Not Disturb when you are not hobbying
If you truly don't want to have a link with the hobby phone info with your personal devices, then the second device for hobbying would be the best option IMHO.
Just my $0.02