The 12.1 upgrade will be particularly important if you're an iPhone XS, XS Max or XR owner. The new software enables dual SIM support using both the conventional SIM card slot and an eSIM. You'll need an eSIM-friendly carrier for this to work, of course, but it'll be helpful if you travel abroad or have separate work and personal lines. Also, you can now control the depth of field effect on portraits before you take a photo -- no more editing after the fact. And yes, this should address complaints that newer iPhones were inadvertently smoothing out face details in selfies.

Apple hasn't said exactly when the update goes live, but it typically releases updates around 1 PM ET.