As Prince Charles and at least one Quebec politician have learned, cellular telephones may be convenient, but they aren't necessarily private.
Cellphones work by communicating with a network of receivers covering adjacent areas.
But for you to be able to receive calls, the cell network needs to know exactly which cell you're in. If your cellular phone is switched on, it's continually transmitting a signal telling a nearby receiver who you are and that you reside, however temporarily, in its cell. A cell can cover an area of up to a few square kilometers, so anyone who wanted to locate you would have to look for your needle in a relatively large haystack. But it is technically possible. That, however, may be small potatoes compared to future wireless technologies.