I carry one. It's a "prepaid" plan, I don't give out the number, I don't keep it turned on. It's for outgoing calls only; I use it on occasion when I need to exchange information with someone while I'm not in my home (e.g. I'm running late) and would use it if G*d forbid I got into trouble of some kind while in my car or whatever. For that, I consider it to be a useful tool. But if I'd never seen one I wouldn't miss it.