Can I add a business line at my home address

Probably but you’ll need to call or place an order to find out. I actually had a second business line paid by my employer at home for many years. I even converted my home phone to digital while leaving that second business line on POTS during that time.

I once had a second POTS telephone line on a separate account that I was reimbursed for, but that was with a company that has since been purchased by AT&T.  If you can order a POTS line at all, then I think that you can probably still get a second account for it.  Note, however, that AT&T is limiting their new technology Internet (a/k/a "U-verse type accounts") to one per physical address.