Re: 2nd incoming line
Not sure if you be able to get a business line from VM if you're on a residential package already.
Have you considered using a voip line over your broadband connection? If you look at someone like sipgate then your line rental would be zero and if you only want it for incoming calls you would never need to add credit to the account. You can set up a voip line with either an analogue telephone adaptor or a voip phone, both of which connect to your existing router.