Apple unveiled the iPhone Duo, its first-ever foldable smartphone, at its annual product launch event on Wednesday in Cupertino, California, following months of mounting anticipation.Presented by CEO John Ternus, the sleek, passport-style device stole the spotlight at the Apple Park event. Ternus, who took over from Tim Cook on September 1, said the handset would “redefine the experience of using a foldable phone”.Starting at US$1,999 – or HK$17,499 (US$2,231) if bought in Hong Kong – Apple’s most expensive iPhone to date comes in cheaper than industry estimates, despite soaring component costs. In mainland China, the device starts at 15,999 yuan (US$2,384), rising to 26,499 yuan for the top-tier model.“[The] iPhone Duo … is Apple’s attempt to frame foldability as a complete premium experience, rather than an experimental hardware feature,” said Francisco Jeronimo, vice-president for worldwide client devices at IDC.“Apple showed up years after everyone else … [but it] set the price and the standard every rival will now be measured against.”Here is what you need to know about Apple’s landmark product launch, and the caveats facing buyers in mainland China.