[Update] Itseems like recent software updates on the Gear S2, have brought an end to this direct pairing with the iPhone. We'll have to wait for some more time for an official update.
During CES 2016, Samsung had announced that they would soon push an update to the Gear S2 making it compatible with iPhones. Now, if you're one of those people who's been waiting for that specific update to roll-out before purchasing the Tizen powered smartwatch, then here's a temporary way in getting essential services to work on the Gear S2 when paired with an iPhone. This method surfaced on an YouTube channel going by the name Anmadas and involves just pairing the Gear S2 from the iPhone's settings menu via Bluetooth.
Pairing the Gear S2 on Android smartphones requires the user to download the Gear Manager App which controls all the functionalities of the smartwatch and allows the user to install new apps on the Gear S2. The direct pairing method on the iPhone won't be letting you do that and has very little control on the behavior of the Gear S2. When paired with an iPhone, as described in the Video the Gear S2 can show notifications, Caller ID, initiate calls, read and write sms messages and a few other services. While, buying nearly a $250+ smartwatch to get the same features as on a $50 smartwatch wouldn't make any sense for an iPhone user, one has to keep in mind that the Gear S2's full support to iOS devices is right around the corner and will probably be coming up with a Gear Manager app on the app store to control all the possible aspects of the Gear S2.