does anyone know why my mp3s are locked??

Purchased music files are not mp3's, but protected MPEG-4 audio files with an .m4p extension.
Because of the protection, they cannot be converted to mp3.

If your phone only accepts mp3's, you have to perform a few steps to convert them.
Burn the files on Audio CD.
Import the Audio CD in mp3 format (choose MP3 Encoder in Preferences>Advanced>Importing).
Now you will have two copies of the same song in your library.
To distinct them, add (if not done already) the 'Kind' column in 'View Options' (in the View menu).
The mp3 can be identified as 'MPEG audio file' and the purchased song as 'Protected AAC audio file'.

Hope this helps.

M

17' iMac 800 MHz, 768 MB RAM, 200 GB HD, DL burner Mac OS X (10.4.7) iTunes 7.0

These are probably not MPEG 1 layer 3 (.mp3) files but are instead Protected AAC (.m4p) files. Select the file in question in your iTunes playlist and select File > Get Info to find out.

You'll have to perform a web search to find out how to subvert the tyranny of DRM, or just wait another few months for the new Apple phone.