You can manage your vm greeting both from the phone and from the Google voice web site. I have set up a custom greeting set up using the web site. It calls your phone for you and then you record into your phone. My custom greeting works. I tried to change my greeting directly from calling my Google voice voicemail number from my phone and it told me that I still have the "System standard" greeting. Because that is incorrect I just hung up. If you are not already try managing your greeting from the web site.