Are you sure they are MP3's on the card? One of my techs has this phone as well and he bought the music essentials software. He said that it converts the mp3 to a wma while sending it to the phone. He said his the music essentials software is a plug in for windows media player.
I just went to check using sync on my phone and when my computer popped up the message what I wanted to do I told it to go to file explorer. File explorer showed that I did indeed have the MP3's I downloaded from the web on the phone storage card as MP3's. However, the ones from CD's using the windows Media player were converted to WMA. The one I ripped yesterday from different software was saved as an MP3 and did sync using the music essentials software as an MP3.
Not only do I have MP3's on my card but I have been able to use my MP3's as ringtones using BitPim and the data cable. I copied my MP3's and pasted them in the folder ringer in BitPim and then did the send data to phone making sure I checked add ringtones. (BitPim is freeware and if you do a search I'm sure you'll be able to find where to download it to your computer.)
I was getting frustrated because I couldn't get the front buttons to work to play my music. O.K. I wasn't holding the play/pause button long enough to activate it. I'm a happy camper now. If you have version 3 firmware on your phone you will not need to setup the buttons on front so there will be no option in tools for player button. And MP3's are already enabled.