It is important to make sure that the cell phone is wiped clean of any personal information and files such as call logs, address books, text messages, photos, videos and anything else you may have stored on the phone.
The SIM card, if the phone has one, should be removed and the phone's physical memory should be cleared as well. Any expandable micro SD card should also be removed prior to donation.
The cell phone service for the phone should be canceled or disconnected before donation. This can be done by contacting the cell phone service provider. If you are replacing the phone with a new one, the carrier will switch over your account to the new phone. Do this before donating the cell phone.