Google will soon roll out changes to Voice intended to prevent unauthorized access to our voicemail inboxes. To access accounts via phone, you will now have to call from a verified forwarding number. If you're calling from a number Google doesn't recognize, you will be prompted to enter a verified number instead. In addition to this, PIN codes can now be up to 10 digits long. These changes will take effect starting on the first day of October, and anyone who signs in via a web browser should receive a notification giving them a head's up.

If you want to tinker with your phone forwarding or voicemail settings before these changes take effect, here are instructions for doing so straight from Google.

Click Settings at the top of the page. Select the Phones tab. Select the Edit button under the phone for which you wish to change voicemail settings. Click the Show advanced settings link. In the Voicemail Access section: Select 'Yes' to have direct access to voicemail when calling your Google number from the phone in question. When you call your Google number from that phone, you will connect to Google voicemail. You may be prompted to enter your PIN, depending if you've selected the 'PIN required' radio button.

Select 'No' to have the call ring through to your other phones unless you press * and enter your PIN to check voicemails from this phone. Click Save to save your setting.

Source: Google