I used to do Panasonic systems, as mentioned above they can be complicated as there are so many features built in that have nothing to do with small residential systems. And if you don't do them regularly, forget about it. It will feel like you have to learn the programming everytime as it is too easy to miss some setting. I eventually started just using the programmer from the distributer we bought them from.
A few years ago tried talkswitch, which became Fortinet or Fortivoice. They were much easier to set up, sort of geared to the small business guy that could manage things on his own if he wanted.
Now I am dealing with clients asking about what needs to be changed because they want to get rid of their landline and old phone systems. People just use their cell phones now.
It seems to be a common theme, the only people that call us on a land line are telemarketers.
The only time we used the landline was to order take out, and even that is being done more and more on a computer.