The Apple Watch Series 3 adds LTE but at a cost to older iPhone owners — the iPhone 5s won't be able to set up or communicate with the device at all.
Shortly after the Sept. 12 unveiling event, Apple updated its product page for the Apple Watch to reflect the new unit, and the removal of the Series 2. As part of a footnote at the bottom of the page, Apple notes that while the iPhone 5s on iOS 11 can still be used to configure and communicate with the still-available Series 1 Apple Watch and the Series 3 Apple Watch without LTE, but the iPhone 6 and newer is required to configure the LTE version.
It is unclear why the LTE version needs the newer phone to work. AppleInsider has contacted Apple regarding the specific reasons for the iPhone hardware limitation, and will update accordingly.
The Series 3 Apple Watch was demonstrated during Tuesday's iPhone release event, and now features a LTE radio for phone calls and ultimately Apple Music in conjunction with the wi-fi and Bluetooth for communication. The Series 3 watch without LTE is available for a starting price of $329, with the LTE version selling for $399 and up.