A locked cell phone is set up to work only on one carrier’s network. An unlocked cell phone can be linked to the person’s carrier of choice.
Both work on GSM network carriers. GSM stands for Global System of Communication. You’ll need a SIM card from a GSM provider.
CDMA stands for Code Division Multiple Access. Older phones using CDMA technology can’t be unlocked. If you’re buying a CDMA phone, make sure it is already unlocked.