Actual occurrence, GSM/3G device left in transmit. Device while searching for a carrier (inflight) caused interference with the pressurization system. System operates on AC (400hz) voltage, GSM with its known ability to interfere with audio systems appeared to cause enough distortion in the frequency that the outflow valves began to cycle (hunt) causing a mild fluctuation in cabin pressure. After the device was restored to flight mode, no further issue.
GSM devices can broadcast with an initial pulse of over 2watts but then drop down to tenths of a watt. These devices if placed near speakers will cause an aural distortion in the aicraft systems.
Autopilot systems being AC controled could be affected depending on the proximity of the servo's to the GSM transmitter.
What you essentially cause is a VFD or Variable Frequency drive effect in the system since they are intended to run at only a specific frequency.