Hello,
I had this set up and working once before but stupidly erased my configuration and cannot find the appropriate advice after searching and looking through many threads.
This is the deal:
I have a Google Voice account set up on SP4. I would like this to forward all calls to my cellphone but go to Google Voice voicemail if I don't answer. I can't set it up through Google Voice the official way because I already have more linked accounts than I should.
I think last time, under SP4, I just checked CallForwardUnconditionalEnable and then wrote some letters and a number under CallForwardUnconditionalNumber. Maybe I'm wrong but pretty sure I did not touch Line1.
I don't have anything to give in return but you might like this picture of my cat:

Thanks!