Well, that cell phones interfere with monitors, audio equipment etc is pretty well known. A few months ago I got an old Alcatel OneTouch Max GSM phone that interferes with itself while talking! You can actually hear the pulses.
The reason the Nextel phone cause more interferience is because the transmit at a higher power, Motorola did this so they could spread the towers out more. Every time I use my Nextel I can feel the tumor growing......