No, not the sexual kind of personal vibrator. Today we regularly hear reminders to put phones on vibrate, and they are often ignored. The world is becoming rapidly swamped with loud, deliberately destracting cell phone ringtones. (The ringtones themselves are a business.)
I remember visiting Hong Kong 10 years ago, and a business lunch was a serious cacaphony of pagers in a crowded restaurant. They were going off ever few seconds, and this was acceptable there. I don't know how much worse it has gotten. I was on the train today and since that's a place people actually expect to take calls, ringing was quite regular.
Perhaps it's time to declare that cell phones should no longer ring at all, except in certain special circumstances. That the very idea of a ringer should be viewed as rude and pointless and in fact an invasion of your own privacy. Why should the world know you are getting a call?
To make this happen, I propose bluetooth based personal devices to be worn on the body. The most obvious one would be your watch. However, bluetooth based vibrating devices could be placed in glasses, belts, shoes, shirt collars or wallets. Anything the always-available wear on their body. Shoes and belts have the most potential for long battery life. Yes, you would have to charge your device once a week.
The vibrators would have a temperature transducer to know if they are indeed on the body. If that goes cold, a slowly rising ring could be issued from the device or the phone. The phone could also ring if the vibrating sensor is off or not connected to the phone. Or if the phone detects it is in a private car and plugged into car power, though frankly by this time we should all have cars with bluetooth handsfree anyway.
The phone itself, using temperature and other metrics, can also figure out if it is in a pocket, though this works mostly for men. Women tend to keep phones in purses.
Next step -- your cell phone should warn you when you are yelling. It knows if it is getting a good audio signal from you compared to ambient noise. As you probably know, people tend to talk loudly on cell phones if they are having trouble hearing the other party. Your phone should notice this, and give you some subtle "be quieter" tones. If you are using a headset yourself, the phone display could run a VU meter for constant reminder.
(Unfortunately most phones today shut down the backlight and even the processor in the phone during a call to save power, making this harder.)
Here's to a more peaceful public world.