This unit is marked with the numbers 831810377311?, kind of hard to read and I don't know what the numbers represent if anything. The tag on the bottom of the phone reads....
"Serial # 255438
The Telephone housing is your property. To assume quality of service, all working parts, e.g., dial, cords and electrical components remain the property and responsibility of the bell telephone company."
There is some wear on the head set which is normal for it's age. I'm thinking this unit is from the 1970's, but I am not certain. Unit has been connected to a live phone line and works. I even placed a call using the rotary dial and the call went through.