You now can get Google Voice with a Google number OR with your existing mobile phone number. If you choose to use Google Voice with your existing number, you won’t get some features (like call screening and recording), but you’ll still get many others — including Google voicemail:
If you already have a Google number, this new feature should also help with the transition to your new number, as you can now forward unanswered calls to your mobile phone to your Google Voice account. This way, people who still call your old number will reach the same voicemail as people who call your Google Voice number.
If you already use Google Voice, you can add Google voicemail to any mobile phone you’ve linked to your account. If you’re not using Google Voice yet, you can request an invitation or ask someone with a Google Voice account to invite you. When you receive the invitation to sign-up, you decide whether you’d like to use Google Voice with your existing number or get a Google number.