MP3 real ringtones
That is the user manual
Page 43 discusses how to set a ringtone
Page 110 is the start of the section explaining how you can compose your own.
The Fusic LG 550 is capable of the following:
Ringer Types: MIDI, QCELP, MP3, AAC, AAC+
MP3 Ringer: Yes
Animated Ringer: Yes
Video Ringer: Yes
Video Codecs: MPEG-4, H.263, and H.264
Use the data cable and CD that came with the phone to load those files to your phone the when setting a ringer compatible file types will be located in the My Content folder.