I want to convert a particular audio file into a ringtone available for purchase at metroSTUDIO storefront, and was wondering if anyone knows how?

i dunno about that site,

but these days phones just play mp3s./wavs etc straight up..

You will want to very harshlly eq the track, possibly even remake it so that it fits well in the narrow frequency respons of the mobile phone speaker though. having any bass at all will completely kill the max volume of the ringtone..

I suggest at least a lowpass filter + a bit of hipass filter (somewhere on the net you should be able to find some guide to what frequencies work best, I just made a bunch of tests up and played them through).. but also some accentuating of main parts/etc should help too.. also you will notice some sounds have too much texture and need to be simplified - if you dont have the original source material to rebuild the sounds, bit crushing can help to reduce the complexity of some things.

i don't have the exact setup I used, but similar to what cartesia is saying I have a project in Reaper setup for this.
Basically big EQ cut/filter below 300 and above 3k (or something like that), then you render as a 64kb mp3 or something - sounds pretty good to my ears for a phone.
If you are interested i can render a sample

cartesia,

thanks for the suggestive feedback. I actually did several EQ mixes, adjusting the sound to be more mid and high friendly so the frequencies would sound good on a phone. I even played different mix downs of the audio file in .mp3 format on a few different phones to hear the difference.

I seen that Reverbnation allows you to sell ringtones quite easily through an artist's Reverb Store. I would probably use that route to hustle them.