One of the S-76 aircraft I fly IS definitely affected by "live" phones in the aft baggage bay. The smoke detector goes off as the aircraft progresses across the sky and the phone changes to the next "cell", or if a call is received and the phone rings. Because there is no fire extinguisher in the baggage bay, it is a potentially serious issue, especially if IFR (land asap). We always explain this to to passengers in the safety brief and tell them to make sure they don't leave a live phone in a coat or bag.