i did read this post at avherald:
mobile phone
By CRJ900pilot on Tuesday, Feb 17th 2009 17:31Z
Mobile phones DO interfere with equipment. If passengers sit in a row where the wingtip is visible and their mobile phone is on, often you will get "EFIS COMP MON" caution messages.
The wingtip is the location where the magnetic inputs to the AHRS and IRS are being received from. The caution messages indicates a difference in readings between the left and right side. I have had to discontinue a CAT2 approach in the past because we received a message like that at 150ft above the ground. To find out, there were two passengers that decided to power-up their mobiles early since we were landing. Thanks a lot.
Rgds, CRJ900-driver
Any other pilots who can confirm this?