Doug ,
When I was a kid ( a while back) I had an Aunt and Uncle that lived in Bellville NJ . My uncle made molds for plastic products. He was a part time employee for BOTH Western Electric and Lionel Electric Trains. I have a 302 that he made on my birthday in 1946 it has the "S" prefix . I do not not know if it is factual or if I'm correct , but I always assumed it was an indicator of where the factory he worked in was located.....Succasunna , NJ.
Maybe there is someone out there that knows the facts. By the way the 302 he made for me , which I still have , it's a very golden ivory color ...it was made that way not aged .
Sorry I can't ask My uncle as he is long gone.
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Good luck . nice phone
ANDY F K1WI
PS I do know that Succasunna had a long time involvement with the Bell Sytem ESS SERIAL #1 was in Succassauna. This might have been a temporary production line as until 1947 WE plants were only in Hawthorne ,Kearny ,and Baltimore.