Samsung Rant SPH-m540 User Manual page 131

DO NOT turn off or restart your computer, or put it
into standby mode, while using a mass storage
device. Doing so will result in loss or damage of data.
While you are connected to the computer, your
phone's screen will display "Phone Off." You cannot
make or receive calls.
If you connect a mass storage device to a peripheral
device, your device may not work properly.
Section 2J. microSD Card 115