The location used in the MAD MEN episode is actually a redressed old House of Pies on Sunset Blvd. in Hollywood, California, with some added CGI work. Look closely and you will see palm trees found nowhere in upstate New York. (via Howard Johnson’s on Mad Men: It’s Not a Destination, It’s on the Way to Someplace - The Foodstuffs of Mad Men - Eater National)
I can buy House of Pies for the interiors, but where did they find the HoJo’s neon sign? (Seen in the shots of Don calling from the phone booth at night.) I’m thinking, old still or file footage from Howard Johnson’s advertising material, digitally enhanced.
ETA: I loved Howard Johnson’s when I was a kid (ice cream and fried clams, yum), but I was the only family member who did. And I loved HoJo’s when I was sixteen and my car died on the Interstate at night; I ran the rest of the way across the bridge to the HoJo’s on the other side to call for help.