Your access number (non-Google number)
Your access number is the number you see in the bottom left corner of the Google Voice page. This number allows you to access any new voicemails you've received at any time; just call the number from the mobile phone you've linked to Google Voicemail
When calling your access number to listen to your new voicemail, you may be required to enter your PIN, depending on the 'Voicemail access' settings you've enabled on the Phones tab of your Google Voice Settings page.
You may want to set your access number on speed dial on your mobile device(s), for easy access to new voicemails you receive through Google voicemail.