This is a really great trick. It seems obvious, but I never thought about it: You can use the volume up button on your headphones cable or Bluetooth headset to snap a picture with your iPhone.
It's pretty simple: just connect your headphone cable with volume control or pair your Bluetooth set, open the camera application and, presto, you will be able to take photos by clicking the + button remotely.
This is perfect for taking photos on trips without having to use a camera app with a timer. Just use a GorillaPod to position your iPhone and a Bluetooth headset as the clicker (which to me is the only use for these hideous devices now). And I can't wait to get into the subway today to try the cable technique.