Many devices offer a "toll-saver" function for this purpose. Thereby the machine increases the number of rings after which it answers the call (typically by two, resulting in four rings), if no unread messages are currently stored, but answers after the set number of rings (usually two) if there are unread messages. This allows the owner to find out whether there are messages waiting; if there are none, the owner can hang up the phone on the, e.g., third ring without incurring a call charge.