If for some reason you want to have your smartphone's LED flash blinking when you have an incoming call, then boy do we have the app for you! It is called Flash Blink and is a homebrew creation, so don't go looking for it in the Android Market
The app's creator, XDA Developers member faiyyaz, actually made Flash Blink because of a user request. The app itself is pretty simple, but it serves its purpose just right, and additional features may be included in its future releases. Flash Blink has been tested on a Samsung Galaxy S II and is compatible with Andorid 4.0 Ice Cream Sandwich too.
If you want to install Flash Blink on your Android device, you have to follow the link below in order to download it. Also, don't forget to enable the installation of software from unknown sources
by going to the Settings -> Security menu on your device.