Does iPhone 5 have a low battery warning tone? My friend has an iPhone 5 (Verizon), she hears a low battery alert tone when on a call at 10% and 20%. My iPhone 5 (Sprint) has no such tone, anyway I can't find how to enable it if it does.

So if a Verizon iPhone has a low battery alert tone (trill sounding), why doesn't a Sprint iPhone5 have the low battery tone???
No it doesn't have but you can install "Battery Alert" app and it will enable it.