Like computers, cars and PDAs, cell phones started out as purely functional pieces of technology, but quickly evolved plenty of fun frills to keep their users entertained. Adding a ringtone to your phone is one of those fun frills. A ringtone is most often used to refer to the customizable sounds available on cell phones. A polyphonic ringtone is a ringtone that makes use of polyphony. The first polyphonic ringtones used sequenced recording methods such as MIDI. Such recordings specify what instrument should play a note at a given time, but the actual instrument sound is dependent upon the playback device. More recently, ringtones have become extremely diverse, leading to phone personalization and customization. New cell phones allow users to associate different ringtones for different phone book entries. Taking advantage of these features, a new Ringtone Maker trend has emerged. For example, websites like Phonezoo and Phone Sherpa let users make ringtones from the music they already own (MP3, CD etc.) and upload directly to their mobile phone with no limit on the number of songs uploaded. There are dozens of websites allowing users to download ringtones of all genres to their cell phones for a one-time fee or a monthly fee. Now, it is possible to use digital audio recordings as ringtones. Sales of ringtones represent a huge emerging market and a new revenue stream for the music industry and its recording artists. In fact, music publication Billboard now has a chart for Hot Ringtones with the top entries being downloaded hundreds of thousands of times.