I BELIEVE it is Bell System based on the cord.
VTG Bell System Phone 500 DM Western Electric Rotary Dial Desk Untested Flaw
RARE Vintage Orange Rotary Desk Telephone – ITT Bell System Model 500 Untested
Lt Blue Rotary Dial Desk Phone by Bell Systems Western Electric 2-66 USA CD 500
Lt Blue Rotary Dial Desk Phone by Bell Systems Western Electric 4-76 USA CD 500
Vintage Bell System Rotary Phone Black Color Western Electric System 500-DM
VTG Western Electric Bell System Rotary Dial Telephone Yellow Gold 500 Nice
