It is useful to have one's cellphone behave differently in
different locations - e.g. ring loudly when outdoors,
in the office, or vibrate when in a pocket.
GPS can be used for some of these situations, but isn't
useful indoors or for very small changes in location.
marked paper mats could be left in various
locations - office desk, office drawer, car cubbyhole,
bedside table. The cellphone's built-in camera could
identify which mat it had been placed on by reading a
special pattern printed thereon. The cellphone could
be instructed on how to behave on each mat:
Office desk --> ring quietly if called
Office drawer --> keep quiet
Car cubbyhole --> look for bluetooth car kit, or take a
Bedside table --> wake me up in time for my first