Back in the day, New York phone numbers didn't include a 212 or a 646 or a 917, they were based off of the name of the nearest telephone exchange. The Hotel Pennsylvania (at 7th Avenue and 32nd Street), for example, was given PE6-5000, which was connected to the Pennsylvania (PE) exchange, and served the area around Penn Station. Later, it became 736-5000 (the P and E changing to 7 and 3, respectively), and even later: 212-736-5000. And that remains their number today... it's tough to get rid of digits that Glenn Miller and his Orchestra immortalized.
While the hotel opened in 1919, it did not receive the number until the 1930s, placing the phone numbers age at around 80 years old—according to Atlas Obscura, "it's the longest continually operating phone number." However, according to the skeptics over at Wikipedia, "The exact age of the telephone number, and the veracity of the hotel's claim, are unknown." But the song was released in 1940, so, close enough. As a quick aside, Miller wrote that song because many big band names played in the Cafe Rouge, housed inside the hotel.
In turn, Miller's song went on to inspire others, from Bugs Bunny to Milli Vanilli:
"It also inspired the pun title Transylvania 6-5000, used separately by a Bugs Bunny cartoon and a full-length live-action film. The number was requested in the film Breakfast at Tiffany's, and was also referenced in a mix of the Milli Vanilli song "Baby Don't Forget My Number.'"
It was also used by David Lynch in the third episode of Twin Peaks! We just called the number, and Miller's song played before a recording welcomed us to the Hotel. Give it a shot... it may not be around for much longer.