No matter what phone you are using, as long as it supports mp3, the best solution for you to get free ringtones for your mobile is to visit those free ringtone websites. from those websites you can straight download the ringtones directly into your phone and start using it. Some example of the site are ventones.com and Zedge.com just to name a few. Within these sites, there are probably too much ringtones to be downloaded for free that might keep you busy for a while.
now you know how to get free ringtones for straight talks. Some of the sites even offer you to make or customize your own ringtone. You can adjust bass, treble, loudness etc... So you don't need to worry even if straight talk or any other provider didn't offer free ringtones for you, you can still get it from lots of 3rd party sites for free.