If the cell phones are within 10-12 feet or sometimes even further, I notice the interference… only through the Sennheiser mic, not the built-in camera mics. The other day I was shooting in a conference room at a law office. Lots of people with cell phones and other devices were walking by the room and caused a great deal of interference. Normally I simply ask everyone to turn off their cell phones but in this environment this was not possible.