Before the ever so popular Norstar system from Nortel introduced in 1988, Northern Telecom marketed the Vantage Key system from the early 1980s to the 1990s.
The early handsets were called the Vantage Modular Sets and did not resemble modern day Meridian nor SL-1 Q sets. Instead they were more primitive with black buttons and an oddly shaped handset and everything was shiny beige plastic.
In the late 1980s these phones turned into the Meridian and Unity style with a fixed Hold and RLS button. And were called the Vantage Esprit sets. These introduced the matte finished plastic and early Meridian styled handset.
I remember the early Builders Square home improvement stores used these phone systems but eventually they went to Executone.
Here are some photos I found of this system online. I’ll try and search more for the older phone model.