Apps that have options to change the color of the LED can change the blink frequency on the E4GT. One free App that will do this is called Lightflow. If you set the LED color to WHITE in Lightflow for a particular notification type (like SMS for example), the result will be a rapidly blinking Red LED light. Setting the color to anything but RED, will result in a slow, solid then one short blink Red light. I had never gotten any other colors to work though, although some people have reported getting a Magenta color by setting the color to Green in Handcent.
Just a heads up, but so far, the LED color for notifications in the ICS ROM is blue like the charging light. Still no options to adjust the color or blink frequency though.