Some sites make a distinction between ringtones sent by sms and keypress ringtones. They believe sent ringtones incur copyright fees because it is an actual transmission over the air of a melody while keypress codes are only a set of instructions on how to input the melody and thus, do not incur fees.

To comply with the principles of copyright, use public domain melodies as your ringtones or, if you prefer using pop music, make sure that the site does pay copyright fees to the relevant copyright holders.