There are two types of flash. A full flash and a partial flash. A full flash involves re-writing the phone's operating system.A partial flash is when you basically just reprogram the phone to connect to a different carrier. If there isn't a SIM card, you indeed have a CDMA phone that can be flashed. GSM (Global System for Mobile Communications) phones can't be flashed (like AT&T and T-Mobile). Metro, Sprint, Cricket, Boost, Verizon and many others are CDMA and thus can be flashed because they're not controlled by the SIM card. Unlocking is done in GSM phones to swap networks. It can be done either through network provider or through third party unlocks like Mobileunlocksolutions.com