Well, I have call screening enabled for contacts that haven't been put into a couple of my contact groups... Friends, Family, Work, Personal, etc... and my google voice rings my various phones differently, within the defined contact groups.

If I get a call from someone not in one of my contact groups, I get the usual call screening prompt, but I may decide to save that number with a new contact on my phone, and also decide to create a google voice contact and put that contact into a contact group that rings my phones appropriately in the future, rather than continuing to screen the calls.

Obviously, there's already some duplication of effort, creating a contact in my phone, and also creating a contact in google voice, but being able to manage this stuff directly on my phone, without visiting a 'heavier' website, would be convenient, if the Google Voice APIs provide access to these features.

I really don't spend a lot of time on the phone, or receive many calls from unknown callers, but for example... last week I had several unknown callers, while I was taking care of some auto repairs, rental car, upholstery shop, etc.., etc...

The call screening becomes a bit of a bother, if there's a lot of back and forth communication, multiple phone calls still getting screened, etc... before you get around to creating google voice contacts and putting contacts into appropriate call groups.