Hello,
Sorry for being a bit late in my answer. But it's holiday time here and I've been off for some days.
My phone is a S-E K800i and yes , I use a file manager. 2 in fact. The S-E PC Suite + Mobile Master.
As I've written before, when on my gsm, the file has an MP3 extension but when read by my PC it has a FL extension and not an MP3 extension anymore.
Thank.