I did that at home and recently for a customer as well.
Owned Modem (Arris bought at BB), Ooma, and choose your own favorite network gear, I use Araknis. Works like a charm, no "rental fees", and pays for it'self (lack of fees) within a year.
*note, always make sure the residential number gets ported before discontinuing service, as others have said. But once done, this works great, and no Xfinity hotspots, no rental fees, no firmware pushes changing settings, and no calls for service upgrades that confuse the customer (until the plant network gets upgraded: DOCIS3.1 for example), until you're ready to sell the client on new gear or services.