If after switching to iphone 6 your google voice mail all of a sudden stops working, keep reading.
This may have something to do with the new internal settings in iphone 6 with iOS 8. To the general public, simply need to know that the instructions from google voice to dial **004*1[GV-Number]# is not going to work. You would see error messages Setting Registration Failed.
I tried it on my iphone 6 and it works now. Assuming your number is 1-650-789-1234. Simple do this:
1. Dial *#61#
2. Dial *#62#
3. Dial *#67#
4. Dial *61*16507891234# - Call Forward if Unanswered
5. Dial *62*16507891234# - Call Forward if Unreachable
6. Dial *67*16507891234# - Call Forward if Busy
If this is still not working, double check your google voice website and make sure your iphone 6 setting is correct.
Hope this helps!
Ref: http://www.macobserver.com/tmo/cool_stuff_found/post/how-to-make-ios-8-and-iphone-6-work-with-google-voice http://marcelbrown.com/2014/09/22/ios-8-iphone-6-conditional-call-forwarding/ https://productforums.google.com/forum/#!topic/voice/XJt1i0rlm7A