Jesse Hollington, iLounge:

If you have an Apple Watch, you already know that incoming phone calls and FaceTime calls will ring on your watch alongside your iPhone, so you can answer the call and talk on your wrist, Dick Tracy style. Switching the call back to your iPhone once you’ve answered it is straightforward enough as well — simply tap the green bar that appears at the top of the home screen to open the Phone app and transfer the call to there in one fell swoop. What you may not know, however, is that you can also send calls in the other direction — transfer an in-progress call from your iPhone over to your Apple Watch.

Great tip, especially if you have a cellular Series 3 Apple Watch.

UPDATE: As pointed out in the comments, not likely you’ll be able to use this technique to jump from the iPhone’s cellular connection to the Apple Watch Series 3’s own cellular capability. Good point.