Last night my wife wanted to see the photos on her Galaxy S on a computer monitor.

The card reader on one comp didn't recognize the microSD memory card (cheap unreliable Rosewill reader), so I plugged in the USB cable. This caused the phone to automatically
switch itself to USB storage mode. There was a notification that before unplugging the phone <something> should be stopped.

The phone showed up as only /dev/sdl -- no partition number. I mounted it:
mount -t auto /dev/sdl /mnt/cdrom
and rsync'ing the photos and videos in DCIM/Camera to the computer. Then I began to look for this notification, which was gone. After spending some time going through
different menus, there didn't seem to be anything to STOP, so the phone was turned off, USB cable removed, then turned back on.

Everything seemed okay ... it came on to the Home screen. My wife was putting the phone back into it's Trident cover and told me something was wrong. On the screen was an
Android logo and a triangle with ! in it's center. Pressing the Menu button gave some options, such as reboot the phone, restore from SD card, etc. It was similar to the system
recovery options on a laptop.

Not wanting to lose her data or brick the phone, I called C-Spire (our cell service) support. The person who answered the phone had little more clue than I, so I chose to Reboot the
phone. It did, and seems okay. This customer service person did not know how to Stop whatever the notification mentioned. She told me, "We don't know Linux. We're trained on
Windows and Mac only." At least she was honest, and didn't try to baffle me with bull; though I would suspect this option would be the same or similar "on the phone".

The phone is setup to automatically switch to USB storage mode when the phone is connected to a computer via USB cable. Choices there are: Samsung Kies, Mass storage, and Ask on connection. (I haven't read any manual or FAQ, and have no idea what Samsung Kies means.)

My question is: what and how should be stopped before removing the USB cable?

NB: I mount and unmount in a vt (urxvt), not with any file manager. In fact we don't use a DE, don't use any automount software, and aren't going to start now.