Cingular today announced the immediate availability of ringback tones. Unlike ringtones which are heard by the owner of the phone, ringback tones are what is heard by the caller (conventionally a standard ring).
Cingular customers can now set a custom sound as the ringback tone. Options range from Warner Music Group music to sound effects and celebrity voices. Cingular is marketing the new tones as "Answer Tones" and is selling them for $1.99 each. There is an additonal fee of $.99 per month.
Both Verizon Wireless and T-Mobile have had customizable ringback tones for some time.