I recently bought a phone adaptor cisco SPA112. I have to tell you the truth I have at the beginning many problems to get my analogue telephone working. I even call my internet provider and we were a couple of hours without success.
At my home I have telephone connected to internet (IP phone) but before I had a normal phone line. My telephone did not have any ethernet (cable for internet) connection and that is why I bought the cisco adaptor.
I wanted here just write my succesfull experience so that maybe that can help others with similar problems!
I have a Fritzibox modem and my provider is Sunrise in Switzerland. First of all if you have also like me an analogue telephone first try connecting it to the modem with a telephone cable. I came too late to this idea...and in fact it worked and that is a good indicator.
The problem is that I wanted to have my telephone farther away from my modem. To do that you can buy a powerline adaptor that it is just a couple of plugs that take the internet through the electrical network in your house from one plug to another one. In this way I could solve the first issue. But the phone did not work...
Most important advice is that you have to connect to your modem through its internet address in my case in the address fritz.box with password 1234. Then you have to configure a new phone (in Telephone/phone devices) to be operated as IP phone. That solves a lot!! You will find there the user name, the password and the proxy. All these is needed for the settings of the SPA112. Connect to the internet IP adress of your SPA112 and try first in the quick setup to give these parameters, Maybe it will work in this way otherwise you have to check the settings in audio/line1.
I hope this helps a little to the people trying to connect the SPA112.