I have seen a bunch of very complicated processes but all you need to do is log into your Ting account click on Device Settings then select the device. On the settings page for that specific device:
- Uncheck 'Voicemail'
- Check "Forward 'busy calls'... and enter your GV #
- Check "Forward no answer calls"... and enter your GV #
Note that IF you check "Hide my caller ID" then GV won't know it's your phone and calls will ring to you TWICE - the first time and then you you decline the call GV will send it back a second time.