The 1929 Bell System ad is obviously one targeted to a more affluent audience. It most likely appeared in magazines purchased mainly by upper-class ladies.
I would think the subset including ringer would have been mounted to the wall where the maid is plugging in the cord. In a fancy installation, it may well have been recessed into the wall with a grill over it.
As for the intercom feature, there would have been equipment somewhere in the building to provide power, amplification, and signalling for that service. I was in an old house when I was a kid that had such a system at one time. It had long been disconnected by then. An old wall phone was still mounted in a back hallway, and I remember there being some type of switch next to it to select between outside and inside lines. I also remember a lot of old phone wires, and some boxes and connections fastened to a wooden panel in the basement.
My Aunt Doris had intercom on her phones, but that was part of the 1a2 system they had installed in the 70's, which also had two outside lines.
We only had one line, but also an extension in the basement. When we moved into the house in Aug. 1957, my parents had most of the interior of the house repainted. The living room, dining room and hall were painted light gray, so when the phone was installed, my mom chose one in gray - an AE model 80. That was AE's version of the WE 500. The old phone - an AE model 40 in black - was moved to the basement. I always though it was much better looking than the 80. It eventually was replaced with a wall phone, and the phone guy took it away. I found out later on that he had a wonderful collection of older AE phones, which I imagine our old one was among.
As for other color phones, the public library a couple blocks away had an AE 80 in light green.