how to put music on your sidekick 08?

You need files that are in MP3 or WAV format so no iTunes music or WMA or ATRAC or OGG etc.

Next…attach the SK3 to your computer with the USB cable and your computer should recognize it AND your memory card. If you computer doesn’t immediately recognize it check My Computer and you’ll see that you have a new drive (Probably Named Untitled Disk).

Simply click and drag your MP3 files to the memory card and you’re done.

Here is the way it is explained at CNET: Also new to the T-Mobile Sidekick 3 is a built-in music player. It’s pretty rudimentary and supports only MP3 and WAV files, but we still appreciate its inclusion. Using the included USB cable, you simply drag and drop tracks from your PC to the Sidekick, which should show up as an external drive on your PC. Once the files are on your device, you can search for songs by artist, album, genre, or composer, as well as organize tracks into playlists.

Here is how they say to do it on page 86 of your user manual:

Music Player Use the Music Player application to play MP3 sound files that you have stored on your miniSD card. You can use a memory card of any capacity. Remember that you might be sharing the card’s capacity with Camera photos. Copy Music to the Memory Card Before you can copy any songs to your memory card, you must insert a card into the miniSD card slot on your device. For instructions, read “Memory Card Slot” on page 18. Once your card is installed, do the following: 1 Connect your device to your computer with the USB cable provided in the box. Read more in “USB 1.1 Port” on page 19. 2 On your computer, find the mounted USB drive and open it. 3 You should see a folder at the top-level named “Music”. If you do not see this folder, then create it. 4 You’re ready to copy MP3 files onto the memory card. It’s best if you organize your songs in sub-folders under the “Music” folder. For example, you could create one folder for each album or artist. 5 Copy MP3 files from your computer’s hard drive onto your device’s mounted USB drive, in the folders under “Music”, as you wish. 6 When finished copying, close the USB drive window and “unmount” the drive as required by your computer’s operating system. 7 Remove the USB cable from your device and computer.