On my Samsung Galaxy 551 I can remove the MicroSD card without needing to remove the battery and consequently turn off my cellphone. Should I remove my SD without turning off the phone? Will I damage something if I do it?
Yes you will be able to remove the SD Card as Mathew said in his answer. First you need to Unmount SD Card from Settings and then remove the SD Card. In this case no need to remove the Battery or SIM card.
But there are some things that you need to take care of.
1. If you have moved any of the applications to SD Card then you cannot access them without SD Card. 2. Make sure that you are not accessing any of the applications that are installed on SD Card.
After removing the SD Card you can see a status message saying "SD Card removed" in the notification bar of the phone.
You might need to restart your phone after inserting the same SD card back to the phone. Some of the applications might not work. I am sure this happens on 2.1 Eclair devices.