I suggest via memory card, it do support drag and drop. Buy one memory card and card adaptor that can hook in your computer, and then just use the PC studio software, drag and drop the files.. that is Ok.

1)click and drag the music into the adapter file!
2)the adapter was only 10$
3)the memory card pack was around 20$
4) im sure there are cheaper ways but this way worked really well for me!

The answers is that sending email to the phone can not transfer music to a samsung a737,/ before trying to transfer music to samsung a737, you must be sure that you have Windows 2000 or later pc. Not compatible with Mac OS X and A MicroSD card (sold separately) or  USB data cable, and be sure that Ensure music is in .wma, .aac or .mp3 format.

here it the steps from offical att support 

Insert a MicroSD memory card.
Power on the phone.
Connect the handset to the PC.
NOTE: when an active connection is established, a USB icon appears on the phone.

“Connected” displays on the handset.
“Found new hardware” displays on the PC.

When the “Hardware Wizard” appears, click Cancel.

Access My Computer on the PC.

The memory card will be listed under “Devices with Removable Storage” in the same location as an optical drive.
NOTE: The PC will automatically assign a drive letter.

File explore in a new window for desired music files.
Drag and drop the desired music content from the PC window to the “Storage Card” window.

Disconnect the device from the cable.
Access the music player.