How to Change the Ringtone of the Iphone for Calls Coming Forwarded From Google Voice? [Solved]
1. Change your settings in Google Voice so that for Caller ID (incoming) you choose "Display my Google Voice number".
2. On the iPhone, add your Google Voice number as a contact
3. While editing the contact, you can choose a different ringtone than the Default
4. Bonus: if you go into Settings / General / Accessibility and turn on Custom vibrations, you can also choose a custom vibration in 3 above.
Catch: your caller ID will no longer display the caller, but will display your Google Voice number instead. (You can rely on Google Voice Call Screening to find out who it is before you decide to talk to them.)
Another way to change the ringtone of the iPhone for calls coming forwarded from Google Voice?
There are not a lot of options for anyone wanting a separate ringtone other than what Sam suggested.
Given technology improvements, and Google’s introduction of Hangouts, you could try letting personal calls go to Hangouts and all others go to your mobile. This assumes your Google Voice number receives all calls and you are using Google to manage your contacts - something I highly recommend regardless the phone you use.
You would put all personal contacts in a group such as “personal” then in settings you would “forward calls to” Google Chat but not your mobile number.