Instead, you can sign up for a full Google Voice account and get Google Voice voicemail for your existing number--plus preserve the option to use all of Google Voice's other features with a new number if you like. With this option, whether someone calls your mobile phone number or your Google number, Google Voice will handle your voicemail.
Here's how to setup your mobile phone to use Google Voice's voicemail with a full Google Voice account:
- Sign up for a Google Voice account. Note that you'll need an invite to join, currently
- Select the option to create an account with a Google Number rather than a non-Google number
- Add your mobile phone to your Google Voice account
- Go to Settings in Google Voice and click on the "Activate Google voicemail on this phone" link
- Follow Google Voice's popup instructions to forward your phone's voicemail to Google Voice
- Go back to Settings in Google Voice and click the "Edit" link on the settings for your mobile phone
- Click "Show advanced settings"
- Under the "Forwarding Options" section, set "Go straight to voicemail." This will ensure that Google Voice won't try to ring your other phones once your mobile phone has forwarded to voicemail