Call 911 when no other phone is available. If I’m not mistaken, if you have one with GPS, they can utilize that to find you.
Keep in touch with your kids. With a cell, they have no excuse for not calling you, a cab, or a tow truck.
Call your spouse from/at the grocery store. This is HUGE and worth the price of admission by itself.
Receive a text or call from your otherwise silent car alarm that someone is messing with your ride. Disable the ignition or fuel supply remotely, then call the police or vent some anger issues.
It’s a perfect portable alarm clock. 9 minute snooze not enough? Set multiple alarms, 15-20 minutes apart, and specify the days of the week. I have two alarms on weekdays and one for the weekend that lets me sleep in. It’s there when I travel or nap.
There are thousands of others, but those are at the top of my list. My cell phone is my primary phone, which makes it one of the most useful devices I own, because it frees me from being tied to the house – i.e., the mechanic or dog groomer or nanny or whatever can always reach me. I think the trick is knowing when to say when. If you don’t want to talk on the phone all the time, don’t. Leave it on vibrate or ringer off, and don’t use it for business (unless you’re a realtor or some other people-person job, obviously). If I’m busy, I ignore any incoming calls, unless it’s someone I want to talk to. It’s a tool that is always there for me, but I don’t let it intrude.
You can live without it. You can drive back to the store to get the bread you forgot to put on your list. But it does make life run more smoothly.