I have no landlines. When I moved into my home, there was a 60hz hum on my line due to old wires with broken insulation. Moisture gets in and there you have it. When I requested Centurylink (F.K.A. Qwest) replace the cable, they said they would, but it traversed my neighbor's property and given past history, it was going to be a battle, despite telco having a legal right of way. It simply wasn't worth it.
So, I converted from a landline to a burner phone and then onto Google voice, on SP1. I have a 911 provider as well. I did have the need to call 911 a couple of years ago. They answered, they dispatched, my wife is doing well, thank you for asking.
I have Comcast (just can't bring myself to say Xfinity...) and my service is stable. In fact, I have fewer problems transacting voice using the internet than I had with my landline. I have Cell phone service from Sprint and I'm able to call 911 in that manner if my internet service is down. Power goes down more frequently than Internet. I've got a relatively inexpensive UPS. On it are four items. My cable modem, my router, my obi202 and my DECT base station. My alarm system is battery backed up and uses the cellular network for its telemetry needs.
My largest critic in migrating off of Centurylink was my wife.
* What if the internet goes down = cell phones
* What if the power goes down = UPS
* What if it's the zombie apocalypse = KYAG
The first week all of this was running, I was on the phone with her and she says "Oh crap, the power is out...." She just kept talking and at the end of the call I pointed out what should have been obvious, that we were still talking.
This is all about cost vs. benefit vs. risk. The benefit of reduced cost allowed me to mitigate the risk with the UPS and makes me feel better about the money I spend on my family cell phone plan (all unlocked MOTO G at a price that costs you less than taking carrier insurance on your phone over three years, but that's another rant) and my cable internet service. As for risk, I've got first hand validation that 911 works and a fallback plan in case it does not. Do you live in a rural area? Do you have a cell phone?
For the money you spend on two landlines, you could easily rationalize a 2nd obi in case the first one breaks, as well as the UPS.
T