Custom Ringtones
This means that the phone has selectable ringtones that can be set to a custom melody (or "ringer") that you can change to something other than the ringtones included with the phone.
Some phones include a built-in "composer" that let you enter the notes manually and create your own ringtone right on the phone.
Others require that the ringtone be created elsewhere and downloaded to your phone via special SMS, EMS, or MMS messages, or via Wireless Internet.
Ringtones can also sometimes be transferred in the form of a file from another device, such as a phone, PDA, or PC, via a cable, infrared, or Bluetooth.