I have VOIP from AAISP, and it works well. That said, the only person that uses the line is my 85 year old brother who has not mastered FaceTime or Whats App for calls. He does though call me using a basic mobile phone.
VOIP set up can be tricky depending on your router/ATA and choice of phone. It took me about a week of online research to ascertain how to set up push tones on my Gigaset handsets (with a Fritz!box router). AAISP support just pointed me at their support pages which are very technical for a 70+ year old. Gigaset suggested I buy their ATA.
Thanks for getting back to me. Yes it can definitely be tricky, but I have set this kind of thing up before and I have a spare Grandstream ATA knocking around which would do the job. It's just deciding whether to go through the hassle and (minor) expense of getting it all set up... or just risk going 'mobile only'!