In The Great Gatsby, are people really calling from Chicago and Philadelphia, or is this a ruse of Gatsby's to impress his guests?
Honestly, it had never occurred to me before that the phone calls could be a ruse, but it seems possible. After all, Gatsby fakes other things in order to impress people. The bespectacled, owl-eyed man in the library calls him a "'regular Belasco"—a famous theater impresario—as a result of his library full of obviously unread books. The drunken man expresses his awe of Gatsby's attention and commitment to detail because all of the books in his library are real, not cardboard. However, he says, Gatsby "'knew when to stop'" because he didn't cut the pages of the books apart. If the pages are still connected at their outermost edge (as was the practice in book-making at the time), then that means they can't have been read. Therefore, we know that Gatsby has only created the library for show, as though he is putting on a show (like Belasco). Further, he invents an entire backstory, a fictitious and romantic history that he tells Nick, and he even has a medal and photographs to "prove" its truth. In other words, Gatsby lies about a great many other things and in a great many other ways—his name isn't even Jay Gatsby! Why couldn't the phone calls be part of the fiction he has created?
Concerning The Great Gatsby, one would need evidence to suggest that the phone calls from Chicago are a ruse. One would also want concrete motivation for Gatsby wanting to put on a ruse like that.
But in fact, the evidence suggests otherwise. Most importantly, Gatsby is as silent about his work as he can be. In short, he maintains a low profile. His profile is so low that critics have argued about what his business really is. He is likely a bootlegger, but he downplays his business.
Also, Gatsby impresses people through indirect means: his lavish parties and his shirts, which he shows Daisy, are two examples. Personally, he is quite unassuming and shy. Pretending to receive business calls to impress others probably isn't Gatsby's style and is unnecessary.
Finally, it is reasonable and logical that Gatsby owns/runs a business of some kind. His mansion, parties, etc., demonstrate a more than substantial income. Therefore, his receiving a phone call or two should not raise suspicions of his creating a ruse.
Unless you can point to some concrete evidence suggesting the phone calls are fake, the idea doesn't seem to fit the novel.