Is there a product that can take calls from my main phone (Galaxy IV) but is very small?

When I go out on a run I don't want to take my huge hunk of metal on me, but I would like to be able to make or take emergency calls. Is there something that's really small and only has the most basic phone capabilities (take calls, call 2-3 preset numbers)? Moreover, is there such a thing which can take over my existing phone capabilities (maybe by transferring the SIM card, but preferably via app)? Thanks!