Replace the SIM card in your i850!
Use your thumb to slide the back cover locker away from the antenna.
Slide the back cover towards the antenna while lifting the cover away from the phone.
Place your thumb on the indicated corner while stabilizing the phone and the upper portion of the battery with your forefinger.
Lift the battery out of the phone while pushing it towards the antenna.
Place thumb on SIM Card door latch.
Slide the SIM Card door latch away from the SIM Card. The door should pop open. If it does not pop open, use a fingernail to open it.
Lift the SIM Card with your thumb and forefinger to complete the removal of the SIM card!