TrustedReviews have looked at the Sony Network Walkman NW-S203F

I was disappointed to find that a similar tool hadn't been released by Sony for the S203F, but a quick search of Google revealed a clone of MP3FM, but with added features. Not only that, but it works with this model. It's called voidmp3fm and it's available from drvoid.com. It is worth mentioning that it is not officially supported by Sony, but I've had no problems with it yet.

Sony Network Walkman NW-S203F Review