As far as I know, you won't be able to transfer a geographical number to a new VOIP account, but you can get geographical VOIP numbers so you might have to bite the bullet and change your business number to your VOIP. I use Sipgate with the Zoiper app on my phone and laptop, although I've moved out of the area, I still use it and the caller ID always throws people when I ring them from Malaysia etc.
At home, I have a Cisco SPA112 2-Port Phone Adapter with a normal cordless answerphone plugged into it so I can receive messages if I don't pick up incoming calls within a few rings.
It's been very reliable in the several years I've been using it.