Is the Google Chat listed as a forwarding phone on your google voice page?
-If yes, is there a check mark in front of it.
-If no, did you complete the process at gmail and make one successful call from within gmail?
If yes, make sure you do not have anything else running that uses the Google Chat interface. This would include, Talkatone, GrooveIp, and even GMail.
Do the calls go to VM immediately or after the 25 seconds of ringing.