Now, YouTubers in China have created an impressive prototype that shows an iPhone that folds down a central hinge in the screen.
The prototype, called iPhone V, was built by engineers using an iPhone X and the folding mechanism from Motorola's Razr.
iPhone V, which took more than 200 days and thousands of dollars to make, also has silver iPhone lettering on the hinge and the iconic Apple icon on the back.
The engineers admit the result is a pretty 'rudimentary prototype', as it has several issues that became clear after limited periods of use.
For example, there are gaps when folding, and after a few days of use there are horizontal creases and bubbles under the screen that 'can't be fixed'.
What's more, if it's fully closed the whole screen is damaged irreversibly.
It also uses a 1,000mAh battery compared with the 4,352mAh battery on the iPhone 13 Pro Max, so it barely lasts a day.
However, overall, the team claim to have technically created 'the world's first foldable iPhone', potentially years before Apple officially releases one.
Apple appears to have registered patents for a foldable phone, similar to a flip phone, with a horizontal hinge through the middle.
But these were filed years ago, and Apple's recent iPhone models have no design features to suggest it's going down the foldable route anytime soon.
Ben Wood, an analyst at CCS Insight, previously said that there is 'really no need' for Apple to move in the foldable direction at present.
'You can be sure that it has had flexible display technology in its labs for the last decade,' he told MailOnline.
'But at present there is no commercial imperative for Apple to take the risk of piling into a niche market when the iPhone is so unbelievably successful.'
Rival Samsung released its latest generation of foldable phones – the Galaxy Z Fold 4 and the Galaxy Z Flip 4 – in August.
Meanwhile, Motorola released its second-generation Motorola Razr in China this year and is in the process of rolling it out around Europe.
Motorola took inspiration from its original 'clamshell' Razr flip to create the pocket-sized flip phone that folds down a horizontal crease.
Meanwhile, the more recently released Huawei Mate X2 features a dual-screen design very similar to the Samsung Galaxy Z Fold 2.