You get a text message inviting you to download a new ringtone (fashionable song or a tone tailored to the new world events, such as a famous quote or sound). Unless you know who the provider of the ringtone is and how much it costs, never download because you might get a $15 charge on your next phone bill.
Alternatively, you might be asked to call a 1-800 number to get the tone. That will require a credit card and not only will you pay for the ringtone, but you will start being silently charged a high fee every month, as membership. By giving them your credit card number you verbally accepted the enrollment.