I found a player for playing M4a (AAC) files on the Pocket PC. It takes just a little bit of effort to get it to work, the setup is pretty straight forward. You can play these files with the Philips' Platform4 player. Phillips no longer has this file for download or support, but you can still find it at the link below. You will also have to download the patch. After installing the Platform 4 Player on the PPC you will have to copy the "Platform4PocketPlayer.exe" from the PPC Programs file to your host PC in order to apply the patch. After the patch is completed, just move the patched file back to the PPC and start listening to your AAC files. It works great!
Link to download Platform4 Player and Patch-
http://www.rarewares.org/mp4.html
Link for install instructions-
http://www.hydrogenaudio.org/forums/...ic=19742&st=25
Edit- changed AAC file extesion