Idea a Day does what it says on the tin. You sign up and they send you an idea every day by email. Ideas are on all subjects, come from the readers and some of them are very good indeed.
Day 2261
“Equip cell phones to allow personalised vibration sequences so that the user can identify who is calling when the phone is in a pocket.”
Rather obvious when you think about it. Or maybe some phones have it already?
You could hack it using any phone which supports personal ringtones and the iMelody format - iMelody ringtones can also control the vibrator…