This is a hack to get the Samsung Galaxy 3 to mount as a USB drive on Linux. For some reason, it doesn’t react to being plugged in to my computer, apart from a meek beep and an indication that it’s slyly sucking power from the USB port.

• Disconnect your phone from the computer.
• Settings –> About Phone –> USB Settings –> Ask on connection
• Settings –> Applications –> Development: Check both USB debugging and Stay awake.
• Dial *#7284# to open PhoneUtils.
• Set both the UART and USB modes to PDA instead of Modem.
• Connect the phone to the computer.
• You should now receive some sort of USB notification on your phone; you know what to do from here.

This worked for me! Do post in your comments if it worked for you too, or not.

You may need to change the PhoneUtils settings back to the old ones when using your phone as a USB modem.