The hardware store phone number has a 216 area code. At the time period of the episode, that was the area code for Cleveland/northeast Ohio. Mimi lived in Columbus. The area code for Columbus/southeast Ohio was 614.
The actor playing von Braun used the term 'spokesperson.' This politically correct non-word is not known to have been used prior to 1971.
A calendar in the hardware store displays the store telephone number with an area code. In the early '50s, no area code would have been displayed, and the 3-digit local prefix, if displayed at all, would have contained letters.