This could be totally off, but could it be related to switching the third contact on the headphone jack? On my n800, the jack has three contacts: stereo left and right and mic input. On an iPod Touch, I believe the three contacts are used for stereo left and right and video out. This allows the use of external display devices such as those MyVu and Carl-Zeiss LCD glasses. On a new Nokia device, the ECI thing could be a way of sensing which is plugged in so the device can decide to output video or input mic.