Some investigators in the disk drive area have found that under certain test conditions that GMR heads can be altered or damaged if near an activated cell phone. The testing was contrived a bit in that a large coaxial antenna was attached across the magnetic stripe of the GMR head and the cell phone operated within inches of the antenna. Naturally, this sort of condition should not occur in actual practice but it does show that the sensitivity of the particular item was quite high (easy to damage). Of course a charged piece of plastic waved in front of the antenna would have resulted in the same problem or worse. The signal strength of a cell phone should not cause problems to anything of a practical nature. Have a look at papers presented in the EOS/ESD Symposia from 1998-2000 regarding testing of sensitive items like GMR heads for disk drives.
Transforming Technologies