SYDNEY: Sales of Apple’s first folding phone, the iPhone Duo, began on Friday, with ​market watchers betting on whether the device can reinvent the small foldables market just like the iPhone did for smartphones.

The Duo’s reception could ‌prove an early test for new CEO John Ternus, the former hardware chief who unveiled the phone barely a week after taking charge in September.

It could also have large implications for a niche category in which rivals such as Samsung Electronics and Huawei Technologies have sold premium offerings for several years.

Within minutes of pre-orders opening last…