I keep hoping my invite will show up, but no such luck. I've had my gmail account since shortly after the beginning, when people had single digit invites haha...

Anyway, this solution relies on the call actually ringing at the handset. CDMA networks have a simulated ring on the caller's side - I have had a major problem in the past where I had decent service, but my phone would never ring. People who called me would hear it ring the 6-8 times before going to voicemail... and I'd never be notified of it because my phone never rang. In this case, your app wouldn't do any good because the phone never gets notification of the incoming call.

The number of rings before voicemail transfer is different too, because of the delay in the handset picking up the notification of a call... sometimes you'll get it right away, other times there can be a 4 second delay (or even much longer) resulting in a shorter ring time on the handset.

Unfortunately, it just isn't realistic because of Sprint's network :/