Your Avid Trio sports a microSD memory card slot. If your laptop or personal computer is compatible with that card format (Most laptops are so-equipped), you should be able to transfer a music file
The ZTE Avid Trio is an Android smartphone and the Android market offers a bunch of free ringtone apps such as MP3 Ringtone Maker, RingDroid (open source) and more.
Here are some of the free ringtones (compatible with your ZTE Avid Trio) we offer:
Free Horror Ringtones Free Ghost Ringtones Free Ringtones-a-gogo Free Techno Ringtones Hear All Our Free Polyphonic Ringtones