Another helpful little feature would be allowing phones to AT LEAST do the useful PDA things stored on the phone when there is no signal/service available.
I've had a couple of different phones that, when you are not close enough to a cellular tower, you can't even tell what time it is. You can't see your contacts (including emergency contacts). You can't see your calendar (and any reminders you set won't 'ring'). The whole phone is a BRICK, capable only of running a little 'searching for service' animation.
Practically EVERY phone has a 'contacts' list, which IN AN EMERGENCY might prove to be useful (especially if you put in the 'I.C.E.' contact), except it is often inaccessible if the cellular network is down - so even if you find a working phone to call from, you don't have your phone book, and many people have been dialing from a 'contact' list for long enough that they don't remember any actual phone numbers.
The worst part of this is that you can't tell if your phone will be a brick in this situation until you're out of range or in a tunnel, or underground, or even jammed for the first time.