Samsung published a compatibility chart which reveals how Samsung Gear S3 smartwatches works with Android, iOS and Samsung devices. The compatibility chart also shows that Gear S3’s calling, messaging and email features are limited when paired with a non Samsung Android device.
Samsung recommends to use Gear S3 Classic and Frontier with any of Samsung Android smartphones for full compatibility of smartwatch’s core functionalities. However, non Samsung Android device are likely to get limited compatibility on some features like calls, messaging and email.
Samsung Gear S3 smartwatches do no support features such as email and Samsung Pay over Bluetooth using iOS device.
Source from Samsung