Just palyed around with an MP3 and a WMA I was having issue with on my Audiovox SMT 5600 ( Windows Powered Phone )
Anyway I had these 2 files that sounded ok on my home system, then placed on my phone I had trouble hearing on the ear buds, just too soft.
So I fired up Roxio Sound editor and had a go at tweeking the sound.
Tweek and adjust ( added a simple 5 Db and tiny adjustments across the board)
File Saved and tranfered ( finished file )
It worked like a charm, now 100% volume is too loud ( no distortion either ).
Anyway there are many many Freeware and adware sound editors, plus Microsoft offer Win Media Encoder for free ( can adjust sound levels ).
If you have a sound editor I would say run your MP3's and WMA throught to tweek them up a bit for mobile use
I hope this helps someone get better sound form their unit be it a phone or micro MP3 Player, as it helped me a ton!!!
***TIP : Remember kids a little goes a long way, be careful when you up the Db level, too much will kill good sound and could hurt your ears***