Is there a "magic number" I can dial to go to voicemail from a connected phone?
go to your phone's voicemail settings and just change the existing voicemail number to your google voice number.
not sure what this reply means , can you clarify?
All I do is call my GV number from GV
You can call your own GV number to get to the Google Voice voicemail menu. There is also a shortcut code "1186" you can dial to do the same.
"1186#" Works for me.