I was converted to VoIP a couple of years ago, when the BT exchange for the area was being switched off and everyone still with BT had to shift. At the time the sweetner was two basic cordless handsets, one fancy cordless handset or a converter box that would connect a conventional cordless handset system to the BT full fibre router. I went with the cheap cordless handset offer and picked up a converter box on ebay for less than BT wanted for one. If you wanted, a basic UPS with a few hours support was on offer for about 70 quid extra, which wouldn't be much use if the problem happened in the early hours of the morning and took longer than 4 hours to fix!
If you had a health care system, you were advised to contact your provider...
I've not had any problems (so far) with the VoIP system going off. I've got a mobile phone as it is, but as I'm not glued to it at all times, I have to remember to occasionally put it on charge. It'd be my luck for it to be flat if ever the VoIP connection went down!