Play music over wired headphones. Connect to peripherals that use the original wide connector. Talk with dongles that communicate over the headphone port, like those credit card readers.
Oh shit. I totally didn't realize that Apple royally boned everyone using Square readers.
Did they though? Seems like magnetic stripe readers in general are on their way out.
Apple has adapters so a modern iPhone can play music over wired headphones or connect to 30pin devices. These probably also work with these credit card readers. Or get a new one after 10 years, they’re only $50.
Modern iPhones can play music over wired headphones! Sure, not all wired headphones. But then again, the original iPhone can't play music over all wired headphones either.