Indeed, Motorola has done a good job building their pagers so that they'll run a long time on a relatively small battery, because they've got internal timers which shut down even the receive circuitry between transmission cycles; they wake up every so often to listen for pages, then go back to sleep - if they go outside a coverage area, the battery life drops substantially because the receive circuitry is active full-time waiting to find a familiar signal.
I have no information that this technique has been used in cellphones - or will be - but it's already in consumer-grade technology that's been shipping in volume for years now. So it's certainly not difficult to build a wireless device which remains active on very low power, waiting for a signal from its Real Owner to wake up and do something.
The PCS cell phones that I have owned all had this property as well. When there is no coverage, the battery life drops dramatically. However, after about 15 minutes of this, the phone goes into "power save" mode, in which it doesn't listen all the time. -- -- Marshall Marshall Clow Idio Software <mailto:mclow@mailhost2.csusm.edu> It is by caffeine alone I set my mind in motion. It is by the beans of Java that thoughts acquire speed, the hands acquire shaking, the shaking becomes a warning. It is by caffeine alone I set my mind in motion.