*facepalm* You guys, don't do this to yourselves, you're setting yourself up for failure...
All LED's are NOT created equal. Yes they are usually all meant to provide some sort of light, whether it be infrared, visible or ultraviolet. There are low current LED's meant for low power lighting applications and there are high current LED's meant for applications where high light intensity and power is required. Some LED's definitely need a large heatsink to operate at their rated voltage/current so that damage will not occur. Flash LED's are a type of
high current LED, usually requiring somewhere around 500mA to 700mA or more and if left on for too long at their max current, they WILL get damaged, which is why they have to be driven at lower currents when providing light for extended periods of time, but not get damaged. A typical LED used for general purposes may only need somewhere around 10 - 20mA of current and no, they will not be noticeably warm.
Take this LED for example: It's a PhlatLight LED meant for projection TV's.
It has a built in thermistor for use with a microcontroller to
monitor temperature and a copper plate meant to attach to a larger heatsink. Depending on the color, red green or blue, the voltage ranges between: 2.3V to 4.4V typical. Not a big deal, right? Your phone battery can be made to put out any voltage in that range with the proper power supply. However, your phone battery won't be able to power these properly because, you see, they
need an 18 amp current source! Feel free to tell me you can run these LED's at their stated voltage and current with no other heatsink attached for 30 minutes and take no damage...
While the current required to produce a similar level of light to these LED's by an incandescent bulb will indeed be much higher if operated at similar voltages, it doesn't make the requirements for these LED's insignificant.
The LED's in phones don't require currents that high but they do require regulation to keep them within safe specs and they also don't include much of a heatsink to keep temperature down when operating at their max, because they are not intended to be operated at max for long periods of time. The only worry I have about a flashlight app for the phone is that it will drive it at max current constantly. On the Omnia, you can tell a difference between flash intensity and "flashlight" intensity when using the included flashlight function on that phone; the flashlight intensity was always less. It all really comes down to the hardware in the phone and what mode the LED driver circuitry is operated in. LED drivers meant for flash can have both flash and torch modes and as long as the software drives the LED in torch mode when operating as a flashlight, then everything should be ok.