Sonic Lighter for iPhone — a $1 app brings the fire to your iPhone that can be shared with other users to create bonfires. Using a sonic modem, not wi-fi or 3G, users have the ability to “ignite” other Sonic Lighter users by touching the two iPhones together.

How do receive a light from another Sonic Lighter? Make sure the Sonic Lighter is running on your phone and your friend’s phone. Make sure your volume is on a reasonably high setting. And make sure that you don’t have a head-set plugged into either phone. Press and hold the valve (next to flints). Point your microphone (base of the phone) to the receiver (the speaker embedded in the touch-pad) of your friend’s phone.

More info: Sonic Lighter | iTunes link

How to ignite a second phone          Blowing out the flame
Hold Both Valves                                Direct air at microphone