Suggestions:
if the file is a *.wav file, encode it to *.mp3 at something like 128kbps
since it's a ringtone, you don't need the whole song, so make sure it's somewhere no longer than 45 seconds long or so. most people don't let their phones ring that long before answering anyway, and if you do it's because you never heard it ring to begin with.
I made plenty very long ringtones and have been able to send them through verizon before, so if there's a filesize limit, these suggestions should help.
I encode to and from MP3 with CDex. I edit files with Audacity. Both are free and simple.
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