The biggest problem is that VOIP is dependent on the broadband, and if the cable goes out, so does your internet and no internet, no VOIP. Anything that is aerial is subject to outages. They are rare, but, also it there's a power outage, VOIP is out to.
You need either to keep the landline or have a cell phone. Even folks with fiber to the premises have occasional outages when some idiot takes a utility pole out.