Allow me to interject a related experience, which might also serve as a feature request for Google Voice.
Because I'm distributing incoming calls to 2 SIP URIs and a cellphone, I obviously couldn't use GV for the distribution, so I'm forwarding it to a Callcentric DID (okay, so now technically I'm effectively distributing it to one DID, one URI, and a cellphone) where I use their "Call Treatments" to do the distribution, specifically a simultaneous ring.
It worked great most of the time, except when I was in the subway, or the local cell tower was on the fritz or the battery on my thirsty little LG ran out. When that happened, the cell service would announce I wasn't available and hang up. Well, Callcentric has a feature where you can selectively set "Push "1" to accept call" for each destination in the group. I just set that for the cell phone and that fixed it right up. Doesn't matter if the phone is on, off, or out of signal. The SIP lines ring. If you answer with the cell phone, you get a brief message to press 1 to accept. As I'm mostly answering on a SIP line anyway, it's a minor inconvenience at worst. If nobody answers, it goes to GV voicemail. (I had the voicemail on the cell disabled.)
Now, wouldn't that "Push 1" seem to be a nice feature to add to Google Voice?