There's this very good answer on desk phones. This question is about personal cell phones. Many people don't bother carrying their personal cell phone with them and just leave it on their desk (or in their bag which they leave on their desk) and then go somewhere - to a meeting or to help a coworker on another floor. Meanwhile their phone will be ringing, ringing and ringing. Sure, when the person is back, he's "oh, so sorry" and everything but before that happens the phone might have rung a gazillion times and annoy everything out of everyone around. Even if they enable vibration only mode a phone laying on the desk and vibrating makes a real lot of noise.
The best solution would be to somehow nail the phones to people. I have no idea how this can be done in case of personal cell phones. Reaching for the phone and shutting it off or something looks really rude and also sometimes requires finding the phone in the bag which doesn't feel good at all.
What can be done to prevent people from leaving their cell phones ringing on their desks?