We call them mobiles here, not cellphones. We each use them to phone the other phone as a way of finding it when it's lost. It'd be handy to have a sort of mini-mobile attached to keys for the saem reasom.

When out shopping as a way of finding each other, for example in a supermarket. Or to make it easier to go off and then meet again without the hassle of having to fix a time and place in advance. ("I'm by the bookcase in the pub").

Or to check if substitute purchases will do instead.

Handy things. But I'd never use mine for a conversation.